Uvexar
2018-11-23, 09:15 PM
"Oh, you poor dumb elf. Don't you get it? Be a vampire, or a ghost, or an immortal with a paint-by-numbers portrait in the rec room. Hell, even a brain-in-a-jar, in a pinch. Anything to avoid the Big Fire Below." -Xykon
So You've Decided to Become a Lich: Maximizing Safety and Power for Fun and Profit
Lichdom is one of the staples of D&D wizardry, along with owlbears and the Various Body Parts of Vecna. It's something I think every lover of magically-inclined characters has considered in the past. This write-up aims to be a guide for players and DMs alike, on how to deal with lichdom and the circumstances and decisions involved thereof.
For the purposes of this guide, I will be assuming you are either a classical lich (potentially a Dread Necromancer, if your DM was nice) or a Walker in the Waste, both of which depend on their phylactery(ies) for survival. I won't touch on things like baelnorns and vassaliches.
Please see the end of this write-up for corrections to some of the information contained herein.
What is a Lich?
Liches are so much more than undead spellcasters. Becoming a lich is a supremely difficult act of magic, requiring both the ability to create magical items and knowledge of the highest-level spells in the game. Beyond that, it is the ultimate test of willpower. Are you willing to rip off your own living flesh just so you can stay in the game? Are you willing to sacrifice hundreds, perhaps thousands, of people to maintain your own immortality? It is a decision based on your morality, your pragmatism, and your dedication to survival.
Classes of Lich
Very few classes have access to the kind of magic a lich needs to survive. Anyone can, technically, become a lich, given they have 11 spellcaster levels and Create Wondrous Item; generally, however, DMs will also rule that liches need to consume souls to survive. This probably requires trap the soul, imprison soul, or soul bind, high-level spells given to only a few classes. Becoming a lich also requires a certain outlook that some classes favor over others. Here are all the classes that can feed souls to their phylacteries:
Wizard: The classical lich. Wizards have access to both of the SRD soul spells, but not imprison soul. These spellcasters aren't able to dish out as much damage as their cleric, sorcerer, or Dread Necromancer counterparts, but where they thrive is in their lair defenses.
Dread Necromancer: Technically, Dread Necromancers don't actually become liches when they reach 20th level; rather, they gain the undead type, to add onto their lich-like class abilities. However, many DMs will simply rule that a DN becomes a lich, replacing their class abilities with the respective lich ones where applicable. For this reason, this class is very likely to ascend to lichdom at the highest level. While Dread Necromancers are masters of necromancy, they are severely limited in their ability to cast utility and lair defense spells, making them more suited to being world-conquerors and generals.
Sorcerer: Our lord and savior Xykon is a sorcerer, which proves that they can indeed become liches. However, the spell- and feat investment required isn't something many sorcerers are willing to undertake. That being said, sorcerer-liches, with the right backup, can be devastating. Just look at Team Evil!
Cleric: The general flavor of this class isn't conducive to lichdom, which is why it's so rare. However, the Walker in the Waste does exist, and it's probably better than ordinary lichdom for clerics. Clerics who take this line have some great offensive and defensive spells, and can easily create hordes of undead at earlier levels than wizards and sorcerers. Not to mention rebuking and self-healing. Again, however, their class flavor just isn't conducive to a lich lifestyle, which is why I think only the truly ruthless min-maxer will attempt such a build.
Classes with the Spite Domain: Spite, from Heroes of Horror, gives access to imprison soul at the highest level. Classes that have somehow gained a cleric domain, and picked this one, can reap the benefits of lichdom. Each one brings different things to the table, and thus I won't be getting into every one at this time.
Being a Lich
So, you've said the rites, sacrificed Urist McPhylacteryFodder to the heathen gods, and felt the weak meat slough off your white bones. Congratulations, you're a lich! This state comes with several benefits, but also several downsides.
Benefits:
You have undead traits. Say goodbye to critical hits, death effects, mind-affecting effects, and oodles of other bad things that spellcasters hate.
You have bonus combat abilities. These include: natural armor, a touch attack, paralyzing touch, a fear aura, turn resistance, damage reduction, and various immunities. All of these are good, except maybe Fear Aura, unless you're killing peasants.
Lesser "wild" undead won't attack you. You no longer have to take that squicky "Lichloved" feat to make uncontrolled zombies and skellies ignore you. Just make sure other players don't coerce you into giving them access to that feat. You're not one of those icky biophiliacs.
You now have access to some really great future templates. Spellstitching is a great way to get around XP costs for spells, and the Demilich is one of the most powerful undead in the game! As you age, you can also gain access to the Evolved Undead template, making yourself even more powerful.
If your DM is using Taint rules...it may be hard to get levels, but all you need is one level of Tainted Scholar and a big pile of desecrated corpses to gain spells out the wazoo. With no downsides! That is, of course, assuming your DM hasn't nerfed the undead's ability to gain taint without repercussion.
You are immortal as long as you feed your phylactery (under most DMs - hug the ones that give you immortality without condition). That should speak for itself.
Downsides:
You have undead traits. Welcome to the world of no longer making death saving throws. Hide your phylactery well. There's also a much greater chance of you encountering weapons designed to harm you - no one ever crafted a bane of humans blade before. In addition, Turn Undead is now your worst nightmare.
You use Charisma for Concentration checks. This is probably not as bad as it sounds, but for many wizards and clerics Charisma is a dump stat. If you're a sorcerer or dread necromancer, you just peed yourself. (Or you would, if you had the proper organs.)
All of your flesh is rotting away. This will certainly make it hard to pass off as an ordinary person. If you want to walk among polite society, you will need to prepare a disguise.
Your survival depends on the survival of your phylactery. This means that you now have two things you need to protect: your body (if you're wearing magic items; for demiliches, this is a non-issue) and your phylactery. Such protections will be discussed later on down the line.
Your very presence is a beacon for adventurers and loyal servants of the gods everywhere. Be prepared to be attacked a lot, including by clerics, all of whom will have Turn Undead. If you're not high-level enough, don't go sticking your nose into the Outer Planes, otherwise your rotting ass is grass.
The level adjustment of becoming a lich makes it harder to earn experience points. Couple that with XP falloff, and you will end up on a constant search for dragons and high-level outsiders if you want to level up.
You are now, officially, on Team Evil. No more hanging around with the buds, unless those buds are death knights. Everyone hates you, and everyone is instinctively repulsed by your presence.
Personally, I think the positives outweigh the negatives. If you're crafting a phylactery, you're probably surrounded by people who agree with that decision, and will have some allies in your unlife. I think most people will agree with my opinion.
Staying Alive
As an undead, you have no Constitution score, which means that you have no bonus hit points. For your level, you are very, very punchable. In addition, your soul is now tied to your phylactery, meaning you have another thing that adventurers want: a shiny bauble to go with your mangled corpse. This section will be broken into two parts: defending your crumbling, necrotic body; and defending your phylactery.
Defending Your Body
Many of the basic tactics ordinary spellcasters use to defend their bodies still apply here. Contingency is still good, as is Craft Contingent Spell. You should always have a backup scroll or wand in case you run out of spells. However, as a lich, this comes with caveats.
First, as an undead, you no longer have to use items that ward from death attacks/effects or mind-affecting effects. This frees up an item slot or three, usually. You are also immune to physical ability damage and all ability or energy drain, fatigue, and exhaustion. Coupled with your immunity to electricity, cold, and polymorph from lichdom, the defensive-minded caster has suddenly freed up many item slots!
Second, you are undead, which gives you additional defensive worries despite all the things it takes away. You must contend with Turning and Rebuking clerics, for whom a lich is a juicy and rewarding target. While your lichdom does give you some basic turn resistance, it is helpful to find or create items that boost this resistance. In addition, you need additional protection from death, since you no longer have the buffer of death saving throws. You must thus key your contingent spells to be cast when you are near death, rather than when you fall unconscious, since you can no longer be knocked unconscious. Since saving your magic items is more important than saving your body, a teleport spell is good enough for getting you out of danger. Finally, as a creature of the undead type, there exist weapons and spells designed to damage you more than other creatures. It's imperative that you build up spell resistance and armor class to dodge these effects. SR can be easily acquired via Spellstitching, while your natural armor bonus improves over time (via Evolved Undead) but can also be increased with items and feats.
If you are an arcane spellcaster, do not wear armor! Unless you can get both proficiency in that set of armor, and arcane spell failure chance to 0%, armor is just a set of penalties, and another item adventurers will loot from your corpse.
Defending Your Soul
If your phylactery is destroyed, you still have time to create a new one. But if you die in the interim, that's it. Your soul is consumed by the Negative Energy Plane and becomes fodder for emo music in 1500 years. Obviously, it's more important to protect your phylactery before your corporeal body.
The main focus of phylactery defense is going to be keeping people from reaching it. That takes several forms.
The most important defense against encroachment is dimensional lockdown. You have to keep people from teleporting, plane shifting, or dimension dooring to your phylactery. The simplest method is a network of antimagic fields, arranged in a pattern just large enough to hold your phylactery at the center. Alternatively, if you can cast it, dimensional lock is a simple but effective way of doing the same thing. You will, however, require additional spells to mimic the bonus effects of an antimagic field, but it gives the advantage of giving additional space to place magic traps close to the phylactery.
Second, nothing physically protects a phylactery better than conjured walls. Walls of force are good, but the best is prismatic sphere, cast with the phylactery at its center. Depending on how much XP you have access to (trapped or bound souls can give some for crafting!), you may want additional prismatic walls can defeat spellcasters who happen to have plenty of spell slots.
Third, magical traps and permanencied spells. Spell traps are cheapest, and can be reset when the adventurers are dead with a single casting. Using permanent spells is more expensive, but have the advantage of being self-resetting. Magical device traps are probably the most expensive, but if you have the funds, they can be the most expansive and complex. An important thing to remember is that all these effects can be defeated with a sufficiently-powerful dispel magic effect, and thus should be produced in bulk.
Finally, and weakest of the basic defenses, is minions. Intimidating a goblin village into serving you is fine and dandy, but they will be nothing but hassles to high-level parties. As a lich, undead are very in-theme, and you have the bonus of being able to move through uncontrolled undead with impunity. Huge rooms filled with mobs of zombies and skeletons can be effective at slowing down adventurers, making them vulnerable to magical traps and the occasional critical hit by Zombie Extra Number 105. You can also summon and bind powerful outsiders, for meatier and more dangerous threats. If you Spellstitch yourself, gain the spell animate dread warrior (from Unapproachable East) as an SLA, and kill things like clerics with stacked finger of death traps, you can animate undead that have powerful casting abilities and skills. And you can have as many of them as you want, all under your control. Animate dread warrior is also good for those pesky adventurers, and a great way to reward your trusted lieutenants.
Another thing to think about is the art of misdirection. Fill a random room in an old dungeon with traps and monsters and watch the adventurers filter in, only to encounter your Crushing Walls of Symbols of Death trap. Hide your real lair someplace secret, while leaving clues and leaks everywhere to a location which turns out to be just a normal mausoleum. Use that massive wizard's Intelligence score like you mean it!
A Lich's Lair
Everyone loves the Tomb of Horrors. Full of creative and deadly traps, it is infamous as the greatest example of pragmatic lair design. But you can do better.
Your lair will have to fill several roles, all of which will benefit you on your dark road through immortality:
Storage for your phylactery
Treasure vaults
Summoning rooms, for your Dread Warrior minions
Libraries, for scrolls and spellbooks
Minion accommodations
Altars for the religiously-inclined
Laboratories for research/fun
Escape routes
Accessibility and Location
Ideally, you would build your base on the remains of a dead god on the Astral Plane. Barring the occasional dreadnought, or a visit from the githyanki, your lair will be almost inaccessible. However, any location that is unreachable by normal means works. A mote of land in the deep Plane of Fire is nice, as is a location on the Ethereal Plane, in the void between the planets. If you only need a place to put your soul, create a demiplane where you can safely stash your phylactery without care.
Your biggest concern is extradimensional lockdown. If you have the means, you should cast dimensional lock over every inch of your lair, except the parts you want your Dread Warriors and other minions to summon monsters into. These areas should be heavily guarded and trapped against any non-allied creatures entering. For your own entrance and exit, you should only use some sort of main foyer, and proceed on foot/in flight through the rest of the lair. If you can teleport a certain distance away from the lair and enter through a main gate, like in the Plane of Fire example, you should do that.
Your second concern is an assault by a party of adventurers. Adventurers are well-equipped and well-prepared foes, and can summon allies of their own into your summoning areas. Heroes of Battle gives access to Necromantic ballistae, which can animate any dead bodies into uncontrolled undead on the deck of an approaching astral vessel. This is also where your minions, particularly your Dread Warriors, are going to shine, giving you ample time to prepare your personal efforts into destroying the invaders. All of your traps will come into play here, and if you set up your defenses well you should be fine and dandy. Above all, you must keep them from entering your base.
A few notes:
Your most crucial target will be the enemy spellcasters. They can dish out the same save-or-dies you can, and clerics can turn your Dread Warriors against you if they are powerful enough. On the plus side, if you can save their corpses, they can make excellent DWs themselves.
Quantity beats quality every time. It doesn't matter how high the enemy's save bonus is, sooner or later they will roll low enough to fail. There's often no need to upgrade your magical traps beyond your initial setups, and a death effect remains a death effect.
As a corellation to the above, adventurers often possess magic items that protect them from the most harmful of your traps. You should design at least a few mundane but deadly traps within antimagic fields.
Don't ignore the physical effects of certain spells. A shapechanged wizard in gold dragon form plummeting toward you? Place a wall of force in his path and watch the bird go splat. Or place it oriented parallel to his flight and slice him in half. Create platforms of short-duration materials with creation, then summon an elephant onto it to create an Animal Cracker. The Astral Plane is your limit.
You're not an adventurer. Running away is only a net benefit for you. Retreat into your base and set up for the long haul.
Of greater concern is an assault by powerful non-adventurer forces. Ancient dragons are a viable threat well into epic levels, and at a certain point demon lords, mighty devils, and elder elementals may become attracted to your treasures. Against these forces, you need to maintain powerful defenses, and possibly allies of your own. Don't be afraid to make deals! Team Evil is a big, happy family, and if you're worried about your rights just confine your deals to devils and creatures of law. These allies can produce additional dimensional lockdowns, coerce potential threats into submission, and additionally eliminate one possible group of attackers from your threat list.
Inner Defenses
The unthinkable has happened. A party of enemies has breached the sacred ground of your lair, and are roaming the halls, killing your hard-earned minions, and stealing your shiny bits. Did you prepare your inner defenses?
Functionally, your inner defenses are like those put in place to defend your phylactery, but spread out over a much larger area. There should be large rooms of directionless undead, which (if your DM is using these rules) can generate passive Turn Resistance simply by being mobbed together. This makes them harder to kill and more of a hassle for adventurers. Another thing to consider is incorporeal undead, who can pass through 5-foot-thick walls. This means you can hide your phylactery room if you can cast ghostform, but it also means you can create rooms where incorporeal undead can pass through any point and assault the adventurers in the area.
Misdirection also comes in handy here. The adventurers breach your library, but all the books are scribed with Explosive Runes on every page! The real tomes are hidden behind shelving units capable of surviving the explosions from such a massive collection of runes. The pathway to your laboratory appears solid, but it is in fact an illusion, placed over a slippery slide that leads directly into a sphere of annihilation. The teleportation circle all the job notes in the pockets of your minions talk about is not, in fact, the way to your phylactery, but is the trigger for the hundreds of symbol spells scribed around it. Be devious. The enemy must come to you.
If you want to collect the bodies of the dead adventurers (for Dread Warriors, or just display purposes), you will want to avoid traps that violently destroy the physical form. Death effects are your friend, as are direct-damage traps. Be aware, however, that there exist magic items that can protect against these effects. For that reason, as above when dealing with initial defense, hang on to your nonmagical traps, and lay down some antimagic fields.
Following these rules, no matter your style, your lair should become an impregnable wall upon which the bodies of the enemy will break.
Your Journey Beyond Immortality
Obviously, the goal of every lich is to continue to gain more power. But how can this be done? You have a level adjustment, you're probably high-level already, and it's going to be hard to beat being capable of casting shapechange anyway. How can you continue your dark path towards true supremacy?
Big Dumb Minions
Animate Dread Warrior is probably my favorite necromancy spell in the game. Capable of generating an infinite number of powerful slaves for your personal use, its one drawback is the hefty XP cost - 300 per hit die of the target corpse. That's a lot of souls. How can you remedy this situation?
Simple: Spellstitching. There's a bit of a process for this.
Get your wisdom to at least 18, before applying the lich +2 bonus. If you become a demilich, you only need a 10 in wisdom; if you are a Wisdom-based caster, this is a non-issue for you. You need your Wisdom at 20 by the time you spellsitch yourself, otherwise this won't work. Having a Wis 13 and then crafting a +5 tome of understanding nips that in the bud easy.
Spellstich yourself. This will require 10,000 XP - 500 for every point of Wisdom you possess. That's a thousand souls, as per the BoVD rules. You may have to sacrifice some level advancement if you want to hurry the process along - it will take 125 days of only casting soul bind and trap the soul, as a wizard, to gain that many souls. The gold cost - 1,000 gp - is basically a non-issue if you are a lich.
Select Animate Dread Warrior as your 1/day 6th level SLA.
Now, with your newfound SLA, you can create one Dread Warrior per day, without paying the XP cost. This Dread Warrior must be a humanoid that has at least 3 hit dice, and no more hit dice than you do. It gains +4 Str but takes a -6 penalty to Int and a -4 to Cha (minimum for both reduced stats is 3). However, it can keep all its abilities, skills, and any feats it still qualifies for. This means that, if you keep coming up against powerful enemies, you can quickly amass a cadre of elite warriors and spellcasters who are all undead. You can even spellstitch some of them if you like, for even more power!
Alternatively, if you have access to Rebuking, seek out powerful undead to battle. If successful, you can claim some pretty powerful undead, from bodaks to mummies.
A final method of gaining minions is the lovely phenomenon of spawn creation. Spawn creation is an instantaneous effect, remaining constant upon the created spawn until it dies or the spawner dies. What you can do with this is shapechange into a wight, shadow, or similar undead with the create spawn ability, then go to town on some lonely peasant village. Assuming you don't encounter a brave party of adventurers just starting out, you can quickly amass a sea of powerful minions that never leave your service, even after the shapechange effect wears off. This is also known as the "wightpocalypse."
Mighty Templates
Spellstitching has been discussed earlier, but it's worth bringing up again, because along with the level 6 SLA you can get 2 SLAs of each level from 1st to 5th. Use these for spells you cast often but find a drain on resources, such as animate dead or lesser planar binding. They must be from the Evocation, Conjuration, or Necromancy schools, but this leaves a wide area of good spells available for the selection. The template also gives bonuses to saves, natural armor, turn resistance, and damage reduction (specifically for a lich, typically 10/+3, which will stack with your 15/bludgeoning and magic).
However, one of the best templates a lich can receive is the Demilich template. While probably difficult to achieve, it comes with a slew of bonuses and abilities that will make you nigh-unstoppable!
Here's a list of the goodies available:
You lose your natural AC but gain an insight bonus to AC equal to your hit dice. This is amazing.
Assuming you're a Medium creature, you become Diminuitive, gaining the requisite bonuses to AC and attacks.
Your insight bonus to AC also applies to touch attacks. I'm unsure if this also applies to ranged touch attacks, but if true this means you just gained a better-than true strike boost to all rays.
You can fly 180 feet, with perfect maneuverability.
Your touch attack deals 10d6+20 negative energy damage to living creatures, with no saves. You do lose your other natural attacks, however.
You can use the Trap the Soul supernatural ability, which even if the creature saves gives it a minimum of 8 negative levels (2d4*4). Eight creatures can be trapped per day, and these uses are not consumed by failures. This means an easy way to eat souls to feed your phylactery.
Your Fear Aura and Paralyzing Touch are improved.
You can cast all your spells as automatically stilled. (This is necessary for game mechanics, as you're a floating skull without a body, but it's still pretty cool.)
You gain a bunch of good at-will SLAs, from enervation, to greater dispel magic, to both versions of create undead, to all summon monster spells, to harm (which can be used to heal yourself). You can also cast greater planar ally twice per day.
You are immune to all magical and supernatural effects, except shatter (which deals 1/2 the damage a crystal creature would take), dispel evil (which deals 3d6 damage, Fort save halves), and holy smite effects. That caster can sling all the wishes and meteor swarms he wants, he still won't damage you.
Any magical items placed near your phylactery can be used by you as normal, no matter where or how far away the phylactery is. You still can't wear 5 rings, but you can now happily run into the fray, knowing only your soul gems are at risk.
+20 turn resistance.
DR 15/epic and bludgeoning. Epic weapons, for the record, have a +6 bonus or higher. Only the most powerful warriors possess that kind of equipment. Now, vorpal swords can still damage you, but only deal half damage. Depending on the size of the weapon, this can be even better than DR 15.
+10 to all your mental stats. Hello, bonus spell slots, rebuking attempts, and SLA DCs!
Automatically gain the epic feats Blinding Speed, Tenacious Magic, and Automatic Quicken Spell.
Basically, you become a god among liches. While you need almost a million gold and 40,000 XP total to craft your soul gems (aka, a few thousand souls - no big deal if you're shooting at this level), after this point, nothing can stand against you. Ancient dragons, epic casters, even demon lords - all will fall before your wrath. Just don't get too cocky.
Another thing to think about, as you age, is the Evolved Undead template. Basically, every 100 years as an undead, you have a cumulative 1% chance to "evolve." This chance continues to advance even if you evolve and each evolution adds another 1%; so if you live 500 years and then evolve, by next century you will have a 6% chance to evolve that century. Should the DM let you evolve, or you roll luckily, you gain a +1 bonus to natural armor, +2 to Str and Cha, and 3 points of fast healing, as well as one of 12 random SLAs. This is always beneficial.
Leveling Up
Leveling is hard as a lich. With all your level adjustments and with a relatively small amount of threats that can give you XP at high levels, it can become almost impossible. You will have to actively seek out threats, or take the Tomb of Horrors route and deliberately attract powerful adventurers to your lair. This can be potentially fatal.
Despite all that, what can you gain from leveling up?
Well, epic feats, mostly. Starting at 21st level, and every three levels thereafter, you gain an epic feat. Depending on your class, you can gain a bonus feat every three to four levels. These can range in power from bonuses to stats to Permanent Emanations, spell slots of 10th level or more, or even additional Quickened spells each round. Most of these feats are quite good, and decisions will depend on what you want. Typically, liches will take bonus spell slots, magic item crafting feats, and other magical boosts.
Another thing you gain is HD. As a lich, many of your abilities are keyed off your HD, and if you take Spellstitched and/or Demilich these HD matter even more.
Finally, you can continue to level prestige classes if you like. Taking a level in an arcane or divine class (whichever you aren't) and then going Dweomerkeeper will give you, given time, access to the ability to cast 4 spells per day as supernatural abilities. This includes Wish. This means that, four times per day, you can produce a single magic item, without XP or gold cost. For aspiring demiliches, whose soul gems are among the most expensive items in the game, this is glorious. And it's excellent for everyone else as well, who can gain any magic item for no cost whatsoever.
Final Thoughts
Lichdom is a great way to gain greater power and prestige after your corporeal body would have long rotted away. But it comes with challenges that many liches fail to overcome. I hope that with this guide, you can create mighty liches that will benefit your game, or your players' game, for sessions to come.
Postscript
I forgot a few useful things.
First, planar binding isn't the only method of attracting powerful outsiders to your service. Gate is quite expensive, but if you have a hundred souls/the supernatural spell ability of the Dweomerkeeper, you can easily call a pit fiend to serve you for a much lesser risk than that of planar binding.
Second, as Asmotherion pointed out below, you can make your phylactery out of a super cool magical item, like a vorpal sword or other long-term use item. That way adventurers will be less likely to want to destroy it, and it can also count for Phylactery Transference if you're crimped for space.
Third, again according to Asmotherion, be sure to keep some Stasis Clones available at all times. That way, even if your phylactery should be destroyed, and your corporeal form crumbles, your soul will flee to a clone, where you can then repeat the process of lichdom.
Fourth, assuming you can find a retailer, the Book of Vile Darkness gives the cost of a soul in larval form as 250 gp, and that of a soul in an imprisoning object as 200 gp. While these give bonuses to spells of their own, they also function as souls, like any you yourself would capture. This means gate's XP cost becomes a material cost of 25,000 gp - small potatoes for a lich, and certainly a low cost for the binding of a pit fiend to your service. Again, however, you will have to find a Demons R Us at some point if you want to buy these.
Fifth, someone suggested down below that you can simply cast your phylactery into a Leomund's Secret Chest and forget about it. Well...you could. And it would be more effective than almost anything else you could do. But you're a lich, not some common pauper hiding their treasures from their lord. Flaunt your power!
Thanks!
Corrections
Unfortunately, it seems I've made some mistakes. I'll try to rectify them here.
First, the entire premise of my lich-favoring classes list is horse**** going by RAW. Anyone can be a lich if you have Craft Wondrous Item. I let my personal bias towards liches eating souls get in the way of good content. I'll leave it in as a reference point for the more classical-lich inclined classes.
Second, you cannot actually use souls in cast spells, only in crafted items. All that means is you craft a scroll of whatever spell you need to cast that has an XP cost, and you need a lot more souls.
If I find more mistakes, I'll correct them here.
So You've Decided to Become a Lich: Maximizing Safety and Power for Fun and Profit
Lichdom is one of the staples of D&D wizardry, along with owlbears and the Various Body Parts of Vecna. It's something I think every lover of magically-inclined characters has considered in the past. This write-up aims to be a guide for players and DMs alike, on how to deal with lichdom and the circumstances and decisions involved thereof.
For the purposes of this guide, I will be assuming you are either a classical lich (potentially a Dread Necromancer, if your DM was nice) or a Walker in the Waste, both of which depend on their phylactery(ies) for survival. I won't touch on things like baelnorns and vassaliches.
Please see the end of this write-up for corrections to some of the information contained herein.
What is a Lich?
Liches are so much more than undead spellcasters. Becoming a lich is a supremely difficult act of magic, requiring both the ability to create magical items and knowledge of the highest-level spells in the game. Beyond that, it is the ultimate test of willpower. Are you willing to rip off your own living flesh just so you can stay in the game? Are you willing to sacrifice hundreds, perhaps thousands, of people to maintain your own immortality? It is a decision based on your morality, your pragmatism, and your dedication to survival.
Classes of Lich
Very few classes have access to the kind of magic a lich needs to survive. Anyone can, technically, become a lich, given they have 11 spellcaster levels and Create Wondrous Item; generally, however, DMs will also rule that liches need to consume souls to survive. This probably requires trap the soul, imprison soul, or soul bind, high-level spells given to only a few classes. Becoming a lich also requires a certain outlook that some classes favor over others. Here are all the classes that can feed souls to their phylacteries:
Wizard: The classical lich. Wizards have access to both of the SRD soul spells, but not imprison soul. These spellcasters aren't able to dish out as much damage as their cleric, sorcerer, or Dread Necromancer counterparts, but where they thrive is in their lair defenses.
Dread Necromancer: Technically, Dread Necromancers don't actually become liches when they reach 20th level; rather, they gain the undead type, to add onto their lich-like class abilities. However, many DMs will simply rule that a DN becomes a lich, replacing their class abilities with the respective lich ones where applicable. For this reason, this class is very likely to ascend to lichdom at the highest level. While Dread Necromancers are masters of necromancy, they are severely limited in their ability to cast utility and lair defense spells, making them more suited to being world-conquerors and generals.
Sorcerer: Our lord and savior Xykon is a sorcerer, which proves that they can indeed become liches. However, the spell- and feat investment required isn't something many sorcerers are willing to undertake. That being said, sorcerer-liches, with the right backup, can be devastating. Just look at Team Evil!
Cleric: The general flavor of this class isn't conducive to lichdom, which is why it's so rare. However, the Walker in the Waste does exist, and it's probably better than ordinary lichdom for clerics. Clerics who take this line have some great offensive and defensive spells, and can easily create hordes of undead at earlier levels than wizards and sorcerers. Not to mention rebuking and self-healing. Again, however, their class flavor just isn't conducive to a lich lifestyle, which is why I think only the truly ruthless min-maxer will attempt such a build.
Classes with the Spite Domain: Spite, from Heroes of Horror, gives access to imprison soul at the highest level. Classes that have somehow gained a cleric domain, and picked this one, can reap the benefits of lichdom. Each one brings different things to the table, and thus I won't be getting into every one at this time.
Being a Lich
So, you've said the rites, sacrificed Urist McPhylacteryFodder to the heathen gods, and felt the weak meat slough off your white bones. Congratulations, you're a lich! This state comes with several benefits, but also several downsides.
Benefits:
You have undead traits. Say goodbye to critical hits, death effects, mind-affecting effects, and oodles of other bad things that spellcasters hate.
You have bonus combat abilities. These include: natural armor, a touch attack, paralyzing touch, a fear aura, turn resistance, damage reduction, and various immunities. All of these are good, except maybe Fear Aura, unless you're killing peasants.
Lesser "wild" undead won't attack you. You no longer have to take that squicky "Lichloved" feat to make uncontrolled zombies and skellies ignore you. Just make sure other players don't coerce you into giving them access to that feat. You're not one of those icky biophiliacs.
You now have access to some really great future templates. Spellstitching is a great way to get around XP costs for spells, and the Demilich is one of the most powerful undead in the game! As you age, you can also gain access to the Evolved Undead template, making yourself even more powerful.
If your DM is using Taint rules...it may be hard to get levels, but all you need is one level of Tainted Scholar and a big pile of desecrated corpses to gain spells out the wazoo. With no downsides! That is, of course, assuming your DM hasn't nerfed the undead's ability to gain taint without repercussion.
You are immortal as long as you feed your phylactery (under most DMs - hug the ones that give you immortality without condition). That should speak for itself.
Downsides:
You have undead traits. Welcome to the world of no longer making death saving throws. Hide your phylactery well. There's also a much greater chance of you encountering weapons designed to harm you - no one ever crafted a bane of humans blade before. In addition, Turn Undead is now your worst nightmare.
You use Charisma for Concentration checks. This is probably not as bad as it sounds, but for many wizards and clerics Charisma is a dump stat. If you're a sorcerer or dread necromancer, you just peed yourself. (Or you would, if you had the proper organs.)
All of your flesh is rotting away. This will certainly make it hard to pass off as an ordinary person. If you want to walk among polite society, you will need to prepare a disguise.
Your survival depends on the survival of your phylactery. This means that you now have two things you need to protect: your body (if you're wearing magic items; for demiliches, this is a non-issue) and your phylactery. Such protections will be discussed later on down the line.
Your very presence is a beacon for adventurers and loyal servants of the gods everywhere. Be prepared to be attacked a lot, including by clerics, all of whom will have Turn Undead. If you're not high-level enough, don't go sticking your nose into the Outer Planes, otherwise your rotting ass is grass.
The level adjustment of becoming a lich makes it harder to earn experience points. Couple that with XP falloff, and you will end up on a constant search for dragons and high-level outsiders if you want to level up.
You are now, officially, on Team Evil. No more hanging around with the buds, unless those buds are death knights. Everyone hates you, and everyone is instinctively repulsed by your presence.
Personally, I think the positives outweigh the negatives. If you're crafting a phylactery, you're probably surrounded by people who agree with that decision, and will have some allies in your unlife. I think most people will agree with my opinion.
Staying Alive
As an undead, you have no Constitution score, which means that you have no bonus hit points. For your level, you are very, very punchable. In addition, your soul is now tied to your phylactery, meaning you have another thing that adventurers want: a shiny bauble to go with your mangled corpse. This section will be broken into two parts: defending your crumbling, necrotic body; and defending your phylactery.
Defending Your Body
Many of the basic tactics ordinary spellcasters use to defend their bodies still apply here. Contingency is still good, as is Craft Contingent Spell. You should always have a backup scroll or wand in case you run out of spells. However, as a lich, this comes with caveats.
First, as an undead, you no longer have to use items that ward from death attacks/effects or mind-affecting effects. This frees up an item slot or three, usually. You are also immune to physical ability damage and all ability or energy drain, fatigue, and exhaustion. Coupled with your immunity to electricity, cold, and polymorph from lichdom, the defensive-minded caster has suddenly freed up many item slots!
Second, you are undead, which gives you additional defensive worries despite all the things it takes away. You must contend with Turning and Rebuking clerics, for whom a lich is a juicy and rewarding target. While your lichdom does give you some basic turn resistance, it is helpful to find or create items that boost this resistance. In addition, you need additional protection from death, since you no longer have the buffer of death saving throws. You must thus key your contingent spells to be cast when you are near death, rather than when you fall unconscious, since you can no longer be knocked unconscious. Since saving your magic items is more important than saving your body, a teleport spell is good enough for getting you out of danger. Finally, as a creature of the undead type, there exist weapons and spells designed to damage you more than other creatures. It's imperative that you build up spell resistance and armor class to dodge these effects. SR can be easily acquired via Spellstitching, while your natural armor bonus improves over time (via Evolved Undead) but can also be increased with items and feats.
If you are an arcane spellcaster, do not wear armor! Unless you can get both proficiency in that set of armor, and arcane spell failure chance to 0%, armor is just a set of penalties, and another item adventurers will loot from your corpse.
Defending Your Soul
If your phylactery is destroyed, you still have time to create a new one. But if you die in the interim, that's it. Your soul is consumed by the Negative Energy Plane and becomes fodder for emo music in 1500 years. Obviously, it's more important to protect your phylactery before your corporeal body.
The main focus of phylactery defense is going to be keeping people from reaching it. That takes several forms.
The most important defense against encroachment is dimensional lockdown. You have to keep people from teleporting, plane shifting, or dimension dooring to your phylactery. The simplest method is a network of antimagic fields, arranged in a pattern just large enough to hold your phylactery at the center. Alternatively, if you can cast it, dimensional lock is a simple but effective way of doing the same thing. You will, however, require additional spells to mimic the bonus effects of an antimagic field, but it gives the advantage of giving additional space to place magic traps close to the phylactery.
Second, nothing physically protects a phylactery better than conjured walls. Walls of force are good, but the best is prismatic sphere, cast with the phylactery at its center. Depending on how much XP you have access to (trapped or bound souls can give some for crafting!), you may want additional prismatic walls can defeat spellcasters who happen to have plenty of spell slots.
Third, magical traps and permanencied spells. Spell traps are cheapest, and can be reset when the adventurers are dead with a single casting. Using permanent spells is more expensive, but have the advantage of being self-resetting. Magical device traps are probably the most expensive, but if you have the funds, they can be the most expansive and complex. An important thing to remember is that all these effects can be defeated with a sufficiently-powerful dispel magic effect, and thus should be produced in bulk.
Finally, and weakest of the basic defenses, is minions. Intimidating a goblin village into serving you is fine and dandy, but they will be nothing but hassles to high-level parties. As a lich, undead are very in-theme, and you have the bonus of being able to move through uncontrolled undead with impunity. Huge rooms filled with mobs of zombies and skeletons can be effective at slowing down adventurers, making them vulnerable to magical traps and the occasional critical hit by Zombie Extra Number 105. You can also summon and bind powerful outsiders, for meatier and more dangerous threats. If you Spellstitch yourself, gain the spell animate dread warrior (from Unapproachable East) as an SLA, and kill things like clerics with stacked finger of death traps, you can animate undead that have powerful casting abilities and skills. And you can have as many of them as you want, all under your control. Animate dread warrior is also good for those pesky adventurers, and a great way to reward your trusted lieutenants.
Another thing to think about is the art of misdirection. Fill a random room in an old dungeon with traps and monsters and watch the adventurers filter in, only to encounter your Crushing Walls of Symbols of Death trap. Hide your real lair someplace secret, while leaving clues and leaks everywhere to a location which turns out to be just a normal mausoleum. Use that massive wizard's Intelligence score like you mean it!
A Lich's Lair
Everyone loves the Tomb of Horrors. Full of creative and deadly traps, it is infamous as the greatest example of pragmatic lair design. But you can do better.
Your lair will have to fill several roles, all of which will benefit you on your dark road through immortality:
Storage for your phylactery
Treasure vaults
Summoning rooms, for your Dread Warrior minions
Libraries, for scrolls and spellbooks
Minion accommodations
Altars for the religiously-inclined
Laboratories for research/fun
Escape routes
Accessibility and Location
Ideally, you would build your base on the remains of a dead god on the Astral Plane. Barring the occasional dreadnought, or a visit from the githyanki, your lair will be almost inaccessible. However, any location that is unreachable by normal means works. A mote of land in the deep Plane of Fire is nice, as is a location on the Ethereal Plane, in the void between the planets. If you only need a place to put your soul, create a demiplane where you can safely stash your phylactery without care.
Your biggest concern is extradimensional lockdown. If you have the means, you should cast dimensional lock over every inch of your lair, except the parts you want your Dread Warriors and other minions to summon monsters into. These areas should be heavily guarded and trapped against any non-allied creatures entering. For your own entrance and exit, you should only use some sort of main foyer, and proceed on foot/in flight through the rest of the lair. If you can teleport a certain distance away from the lair and enter through a main gate, like in the Plane of Fire example, you should do that.
Your second concern is an assault by a party of adventurers. Adventurers are well-equipped and well-prepared foes, and can summon allies of their own into your summoning areas. Heroes of Battle gives access to Necromantic ballistae, which can animate any dead bodies into uncontrolled undead on the deck of an approaching astral vessel. This is also where your minions, particularly your Dread Warriors, are going to shine, giving you ample time to prepare your personal efforts into destroying the invaders. All of your traps will come into play here, and if you set up your defenses well you should be fine and dandy. Above all, you must keep them from entering your base.
A few notes:
Your most crucial target will be the enemy spellcasters. They can dish out the same save-or-dies you can, and clerics can turn your Dread Warriors against you if they are powerful enough. On the plus side, if you can save their corpses, they can make excellent DWs themselves.
Quantity beats quality every time. It doesn't matter how high the enemy's save bonus is, sooner or later they will roll low enough to fail. There's often no need to upgrade your magical traps beyond your initial setups, and a death effect remains a death effect.
As a corellation to the above, adventurers often possess magic items that protect them from the most harmful of your traps. You should design at least a few mundane but deadly traps within antimagic fields.
Don't ignore the physical effects of certain spells. A shapechanged wizard in gold dragon form plummeting toward you? Place a wall of force in his path and watch the bird go splat. Or place it oriented parallel to his flight and slice him in half. Create platforms of short-duration materials with creation, then summon an elephant onto it to create an Animal Cracker. The Astral Plane is your limit.
You're not an adventurer. Running away is only a net benefit for you. Retreat into your base and set up for the long haul.
Of greater concern is an assault by powerful non-adventurer forces. Ancient dragons are a viable threat well into epic levels, and at a certain point demon lords, mighty devils, and elder elementals may become attracted to your treasures. Against these forces, you need to maintain powerful defenses, and possibly allies of your own. Don't be afraid to make deals! Team Evil is a big, happy family, and if you're worried about your rights just confine your deals to devils and creatures of law. These allies can produce additional dimensional lockdowns, coerce potential threats into submission, and additionally eliminate one possible group of attackers from your threat list.
Inner Defenses
The unthinkable has happened. A party of enemies has breached the sacred ground of your lair, and are roaming the halls, killing your hard-earned minions, and stealing your shiny bits. Did you prepare your inner defenses?
Functionally, your inner defenses are like those put in place to defend your phylactery, but spread out over a much larger area. There should be large rooms of directionless undead, which (if your DM is using these rules) can generate passive Turn Resistance simply by being mobbed together. This makes them harder to kill and more of a hassle for adventurers. Another thing to consider is incorporeal undead, who can pass through 5-foot-thick walls. This means you can hide your phylactery room if you can cast ghostform, but it also means you can create rooms where incorporeal undead can pass through any point and assault the adventurers in the area.
Misdirection also comes in handy here. The adventurers breach your library, but all the books are scribed with Explosive Runes on every page! The real tomes are hidden behind shelving units capable of surviving the explosions from such a massive collection of runes. The pathway to your laboratory appears solid, but it is in fact an illusion, placed over a slippery slide that leads directly into a sphere of annihilation. The teleportation circle all the job notes in the pockets of your minions talk about is not, in fact, the way to your phylactery, but is the trigger for the hundreds of symbol spells scribed around it. Be devious. The enemy must come to you.
If you want to collect the bodies of the dead adventurers (for Dread Warriors, or just display purposes), you will want to avoid traps that violently destroy the physical form. Death effects are your friend, as are direct-damage traps. Be aware, however, that there exist magic items that can protect against these effects. For that reason, as above when dealing with initial defense, hang on to your nonmagical traps, and lay down some antimagic fields.
Following these rules, no matter your style, your lair should become an impregnable wall upon which the bodies of the enemy will break.
Your Journey Beyond Immortality
Obviously, the goal of every lich is to continue to gain more power. But how can this be done? You have a level adjustment, you're probably high-level already, and it's going to be hard to beat being capable of casting shapechange anyway. How can you continue your dark path towards true supremacy?
Big Dumb Minions
Animate Dread Warrior is probably my favorite necromancy spell in the game. Capable of generating an infinite number of powerful slaves for your personal use, its one drawback is the hefty XP cost - 300 per hit die of the target corpse. That's a lot of souls. How can you remedy this situation?
Simple: Spellstitching. There's a bit of a process for this.
Get your wisdom to at least 18, before applying the lich +2 bonus. If you become a demilich, you only need a 10 in wisdom; if you are a Wisdom-based caster, this is a non-issue for you. You need your Wisdom at 20 by the time you spellsitch yourself, otherwise this won't work. Having a Wis 13 and then crafting a +5 tome of understanding nips that in the bud easy.
Spellstich yourself. This will require 10,000 XP - 500 for every point of Wisdom you possess. That's a thousand souls, as per the BoVD rules. You may have to sacrifice some level advancement if you want to hurry the process along - it will take 125 days of only casting soul bind and trap the soul, as a wizard, to gain that many souls. The gold cost - 1,000 gp - is basically a non-issue if you are a lich.
Select Animate Dread Warrior as your 1/day 6th level SLA.
Now, with your newfound SLA, you can create one Dread Warrior per day, without paying the XP cost. This Dread Warrior must be a humanoid that has at least 3 hit dice, and no more hit dice than you do. It gains +4 Str but takes a -6 penalty to Int and a -4 to Cha (minimum for both reduced stats is 3). However, it can keep all its abilities, skills, and any feats it still qualifies for. This means that, if you keep coming up against powerful enemies, you can quickly amass a cadre of elite warriors and spellcasters who are all undead. You can even spellstitch some of them if you like, for even more power!
Alternatively, if you have access to Rebuking, seek out powerful undead to battle. If successful, you can claim some pretty powerful undead, from bodaks to mummies.
A final method of gaining minions is the lovely phenomenon of spawn creation. Spawn creation is an instantaneous effect, remaining constant upon the created spawn until it dies or the spawner dies. What you can do with this is shapechange into a wight, shadow, or similar undead with the create spawn ability, then go to town on some lonely peasant village. Assuming you don't encounter a brave party of adventurers just starting out, you can quickly amass a sea of powerful minions that never leave your service, even after the shapechange effect wears off. This is also known as the "wightpocalypse."
Mighty Templates
Spellstitching has been discussed earlier, but it's worth bringing up again, because along with the level 6 SLA you can get 2 SLAs of each level from 1st to 5th. Use these for spells you cast often but find a drain on resources, such as animate dead or lesser planar binding. They must be from the Evocation, Conjuration, or Necromancy schools, but this leaves a wide area of good spells available for the selection. The template also gives bonuses to saves, natural armor, turn resistance, and damage reduction (specifically for a lich, typically 10/+3, which will stack with your 15/bludgeoning and magic).
However, one of the best templates a lich can receive is the Demilich template. While probably difficult to achieve, it comes with a slew of bonuses and abilities that will make you nigh-unstoppable!
Here's a list of the goodies available:
You lose your natural AC but gain an insight bonus to AC equal to your hit dice. This is amazing.
Assuming you're a Medium creature, you become Diminuitive, gaining the requisite bonuses to AC and attacks.
Your insight bonus to AC also applies to touch attacks. I'm unsure if this also applies to ranged touch attacks, but if true this means you just gained a better-than true strike boost to all rays.
You can fly 180 feet, with perfect maneuverability.
Your touch attack deals 10d6+20 negative energy damage to living creatures, with no saves. You do lose your other natural attacks, however.
You can use the Trap the Soul supernatural ability, which even if the creature saves gives it a minimum of 8 negative levels (2d4*4). Eight creatures can be trapped per day, and these uses are not consumed by failures. This means an easy way to eat souls to feed your phylactery.
Your Fear Aura and Paralyzing Touch are improved.
You can cast all your spells as automatically stilled. (This is necessary for game mechanics, as you're a floating skull without a body, but it's still pretty cool.)
You gain a bunch of good at-will SLAs, from enervation, to greater dispel magic, to both versions of create undead, to all summon monster spells, to harm (which can be used to heal yourself). You can also cast greater planar ally twice per day.
You are immune to all magical and supernatural effects, except shatter (which deals 1/2 the damage a crystal creature would take), dispel evil (which deals 3d6 damage, Fort save halves), and holy smite effects. That caster can sling all the wishes and meteor swarms he wants, he still won't damage you.
Any magical items placed near your phylactery can be used by you as normal, no matter where or how far away the phylactery is. You still can't wear 5 rings, but you can now happily run into the fray, knowing only your soul gems are at risk.
+20 turn resistance.
DR 15/epic and bludgeoning. Epic weapons, for the record, have a +6 bonus or higher. Only the most powerful warriors possess that kind of equipment. Now, vorpal swords can still damage you, but only deal half damage. Depending on the size of the weapon, this can be even better than DR 15.
+10 to all your mental stats. Hello, bonus spell slots, rebuking attempts, and SLA DCs!
Automatically gain the epic feats Blinding Speed, Tenacious Magic, and Automatic Quicken Spell.
Basically, you become a god among liches. While you need almost a million gold and 40,000 XP total to craft your soul gems (aka, a few thousand souls - no big deal if you're shooting at this level), after this point, nothing can stand against you. Ancient dragons, epic casters, even demon lords - all will fall before your wrath. Just don't get too cocky.
Another thing to think about, as you age, is the Evolved Undead template. Basically, every 100 years as an undead, you have a cumulative 1% chance to "evolve." This chance continues to advance even if you evolve and each evolution adds another 1%; so if you live 500 years and then evolve, by next century you will have a 6% chance to evolve that century. Should the DM let you evolve, or you roll luckily, you gain a +1 bonus to natural armor, +2 to Str and Cha, and 3 points of fast healing, as well as one of 12 random SLAs. This is always beneficial.
Leveling Up
Leveling is hard as a lich. With all your level adjustments and with a relatively small amount of threats that can give you XP at high levels, it can become almost impossible. You will have to actively seek out threats, or take the Tomb of Horrors route and deliberately attract powerful adventurers to your lair. This can be potentially fatal.
Despite all that, what can you gain from leveling up?
Well, epic feats, mostly. Starting at 21st level, and every three levels thereafter, you gain an epic feat. Depending on your class, you can gain a bonus feat every three to four levels. These can range in power from bonuses to stats to Permanent Emanations, spell slots of 10th level or more, or even additional Quickened spells each round. Most of these feats are quite good, and decisions will depend on what you want. Typically, liches will take bonus spell slots, magic item crafting feats, and other magical boosts.
Another thing you gain is HD. As a lich, many of your abilities are keyed off your HD, and if you take Spellstitched and/or Demilich these HD matter even more.
Finally, you can continue to level prestige classes if you like. Taking a level in an arcane or divine class (whichever you aren't) and then going Dweomerkeeper will give you, given time, access to the ability to cast 4 spells per day as supernatural abilities. This includes Wish. This means that, four times per day, you can produce a single magic item, without XP or gold cost. For aspiring demiliches, whose soul gems are among the most expensive items in the game, this is glorious. And it's excellent for everyone else as well, who can gain any magic item for no cost whatsoever.
Final Thoughts
Lichdom is a great way to gain greater power and prestige after your corporeal body would have long rotted away. But it comes with challenges that many liches fail to overcome. I hope that with this guide, you can create mighty liches that will benefit your game, or your players' game, for sessions to come.
Postscript
I forgot a few useful things.
First, planar binding isn't the only method of attracting powerful outsiders to your service. Gate is quite expensive, but if you have a hundred souls/the supernatural spell ability of the Dweomerkeeper, you can easily call a pit fiend to serve you for a much lesser risk than that of planar binding.
Second, as Asmotherion pointed out below, you can make your phylactery out of a super cool magical item, like a vorpal sword or other long-term use item. That way adventurers will be less likely to want to destroy it, and it can also count for Phylactery Transference if you're crimped for space.
Third, again according to Asmotherion, be sure to keep some Stasis Clones available at all times. That way, even if your phylactery should be destroyed, and your corporeal form crumbles, your soul will flee to a clone, where you can then repeat the process of lichdom.
Fourth, assuming you can find a retailer, the Book of Vile Darkness gives the cost of a soul in larval form as 250 gp, and that of a soul in an imprisoning object as 200 gp. While these give bonuses to spells of their own, they also function as souls, like any you yourself would capture. This means gate's XP cost becomes a material cost of 25,000 gp - small potatoes for a lich, and certainly a low cost for the binding of a pit fiend to your service. Again, however, you will have to find a Demons R Us at some point if you want to buy these.
Fifth, someone suggested down below that you can simply cast your phylactery into a Leomund's Secret Chest and forget about it. Well...you could. And it would be more effective than almost anything else you could do. But you're a lich, not some common pauper hiding their treasures from their lord. Flaunt your power!
Thanks!
Corrections
Unfortunately, it seems I've made some mistakes. I'll try to rectify them here.
First, the entire premise of my lich-favoring classes list is horse**** going by RAW. Anyone can be a lich if you have Craft Wondrous Item. I let my personal bias towards liches eating souls get in the way of good content. I'll leave it in as a reference point for the more classical-lich inclined classes.
Second, you cannot actually use souls in cast spells, only in crafted items. All that means is you craft a scroll of whatever spell you need to cast that has an XP cost, and you need a lot more souls.
If I find more mistakes, I'll correct them here.