The ideal party to invade the Abyss and slay Demogorgon

[paladinofshojo]

So me and my friends are deciding to do a campaign of new characters to go on a quest to traverse the abyss to slay the Demon Prince himself.

We are currently trying to brainstorm ideas before session zero on which classes will have the best party synergy in mind since we will be literally fighting in the lower planes, there will be 5 of us in the party.

Since the DM said we are going to start off at level 15, we are am assuming he is going to have us go up against the worst that the lower planes has to offer… so right now we, the party are expecting a lot of overpowered BS up against us… as such we want to come up with an even more broken party comp.

Any ideas? My current idea was just all Cleric party, but the rest of the party shot it down for “not being creative enough”.

[Xervous]

You’ve posted in general, we need to know what edition you’re playing!

[KorvinStarmast]

Any ideas? My current idea was just all Cleric party, but the rest of the party shot it down for “not being creative enough”. It seems to be a long standing D&D trope that a paladin will sometimes go into hell to fight demons (https://ih1.redbubble.net/image.1557749851.4248/flat,750x1000,075,f.jpg) (That pic is AD&D 1e vintage)

I'd recommend at least on Paladin regardless of the edition you are playing. If you are playing in D&D 5e I'll double down and say that you need at least one paladin. For example, in order to break up mobs, a paladin of the Watcher Oath can turn a lot of fiends/demons if he keeps his charisma pretty high. (Once per short rest).

(If you are playing a different edition then my advice on The Watcher isn't as useful)

[paladinofshojo]

You’ve posted in general, we need to know what edition you’re playing!

Whoops, sorry, 3.5, my group hates 4th edition with a passion and is slow to warm up to 5 e



It seems to be a long standing D&D trope that a paladin will sometimes go into hell to fight demons (https://ih1.redbubble.net/image.1557749851.4248/flat,750x1000,075,f.jpg) (That pic is AD&D 1e vintage)

I'd recommend at least on Paladin regardless of the edition you are playing. If you are playing in D&D 5e I'll double down and say that you need at least one paladin. For example, in order to break up mobs, a paladin of the Watcher Oath can turn a lot of fiends/demons if he keeps his charisma pretty high. (Once per short rest).

(If you are playing a different edition then my advice on The Watcher isn't as useful)

Yeah, I thought of that too, but since we’re playing 3.5, mechanically, the paladin is somewhat limited in terms of utility…. I am thinking of using the crusader or the pathfinder variant since they do have a bit more flexibility and fill the role of melee fighter with holy magic better than the vanilla one.

There’s also the fact that the quest is to slay demogorgon in the Abyss… which means that being a LG class who cannot associate with evil beings at all or else he’ll lose class abilities will be a liability.

Since the party is assuming that we can at least expect some kind of partial aid from the other demon princes in the Abyss like Orcus or Grazz’t in this quest.

[Xervous]

Oh boy it’s Savage Tides.

Without dropping any spoilers I will broadly detail that the Abyss has all manner of nasties at the high end. You’re going to want everyone to be capable of threatening flying enemies. Immunities and other capabilities can be sourced intelligently through gear, though having at least one cleric offers the party high efficiency on the long duration buffs and the important resurrection service. Optimization can squeeze performance out of most any concept, so you could easily bring a saintly monk like I slaughtered Tippy’s Terrible Trial with. Talk with the GM and other players to be very certain of what OP level you’re operating on. IMO it wouldn’t be a terrible idea to all play gishes.

The party should have skill specialists. There might be sneaky segments, there might be talky segments. That wart on the giant demon’s nose might be shaped like the late king’s face and mean something to those who roll high on knowledge.

Combat wise you can be a little cheeky on gearing. Holy Bane(Demon) Magebane Silver weapons are 50k gp and will chew up pretty much everything you run into down there. +7 to hit, +7+6d6 damage and bypassing DR should provide a good starting point for combat competency without going crazy on optimization.

I’ll circle back around to emphasize your defenses are the most important bit. Protect yourself from statuses and nasty keywords like death effects. Fire and to a lesser extent acid are fairly common. Again, ranged capabilities or at the very least 3D movement are a necessity. Means of preventing teleportation may be critical as one demon teleporting off may bring in dozens more. Anticipate teleportation is an amazing spell to have up as it will give you a bit of breathing room on incoming reinforcements.

Casters, one cleric and one wizard highly preferred. Beyond that I’d lean on Dex Martials / gishes (or zen archers) because Dex builds have an easier time switch hitting, don’t need to jump through as many hoops to gish in their preferred armor, stealth better, and will be packing better reflex saves. Short of layering on optimization, STR builds won’t have extreme consistency on producing full attacks in various environments.

[KorvinStarmast]

Whoops, sorry, 3.5, my group hates 4th edition with a passion and is slow to warm up to 5e Good to know the edition, (this might make a great post in the 3.5e sub forum).


...since we’re playing 3.5, mechanically, the paladin is somewhat limited in terms of utility…. I am thinking of using the crusader or the pathfinder variant since they do have a bit more flexibility and fill the role of melee fighter with holy magic better than the vanilla one.

There’s also the fact that the quest is to slay demogorgon in the Abyss… which means that being a LG class who cannot associate with evil beings at all or else he’ll lose class abilities will be a liability. Great point on how alignment gets in the way here.

Since the party is assuming that we can at least expect some kind of partial aid from the other demon princes in the Abyss like Orcus or Grazz’t in this quest. But of course. Make new friends, or at least allies ...

[paladinofshojo]

Oh boy it’s Savage Tides.

Without dropping any spoilers I will broadly detail that the Abyss has all manner of nasties at the high end. You’re going to want everyone to be capable of threatening flying enemies. Immunities and other capabilities can be sourced intelligently through gear, though having at least one cleric offers the party high efficiency on the long duration buffs and the important resurrection service. Optimization can squeeze performance out of most any concept, so you could easily bring a saintly monk like I slaughtered Tippy’s Terrible Trial with. Talk with the GM and other players to be very certain of what OP level you’re operating on. IMO it wouldn’t be a terrible idea to all play gishes.

The party should have skill specialists. There might be sneaky segments, there might be talky segments. That wart on the giant demon’s nose might be shaped like the late king’s face and mean something to those who roll high on knowledge.

Combat wise you can be a little cheeky on gearing. Holy Bane(Demon) Magebane Silver weapons are 50k gp and will chew up pretty much everything you run into down there. +7 to hit, +7+6d6 damage and bypassing DR should provide a good starting point for combat competency without going crazy on optimization.

I’ll circle back around to emphasize your defenses are the most important bit. Protect yourself from statuses and nasty keywords like death effects. Fire and to a lesser extent acid are fairly common. Again, ranged capabilities or at the very least 3D movement are a necessity. Means of preventing teleportation may be critical as one demon teleporting off may bring in dozens more. Anticipate teleportation is an amazing spell to have up as it will give you a bit of breathing room on incoming reinforcements.

Casters, one cleric and one wizard highly preferred. Beyond that I’d lean on Dex Martials / gishes (or zen archers) because Dex builds have an easier time switch hitting, don’t need to jump through as many hoops to gish in their preferred armor, stealth better, and will be packing better reflex saves. Short of layering on optimization, STR builds won’t have extreme consistency on producing full attacks in various environments.


Yeah, the GM and is have an understanding about this being a “no quarter’s given… no quarter’s asked” game….

We each get to make a level 15 character, and he will essentially have us start off in the material plane, so we are going to have to go through the first layer of Baator, Gehenna, and the River Styx, to reach the Abyss.

I am pretty sure he’s going to have us face off against Zariel and her legions and the Yugoloths and Night Hags too… so it’s going to be a pain.

As such, we are expected to create the most OP story breaking party we can make with 5 level 15s.

Which is kinda why I am of the idea of just making the entire party either wizards/clerics/erudite/artificers and just decimate the legions of the lower planes.

[Elves]

If you're starting at 15 you can just plane shift to the Abyss directly. But can't plane shift to a specific layer without a tuning fork keyed to it IIRC. "Savage Tide" says you can buy the forks for like 10-50k in some places on the first layer of the Abyss.

[paladinofshojo]

If you're starting at 15 you can just plane shift to the Abyss directly. But can't plane shift to a specific layer without a tuning fork keyed to it IIRC. "Savage Tide" says you can buy the forks for like 10-50k in some places on the first layer of the Abyss.

Yeah, we thought about that, but given the unpredictable nature of the Abyss and the fact that we aren’t going to be given any quarter for a screwup we decided that plane shifting straight in would be a death sentence seeing as the DM could port us in the middle of an entire horde of demons.

[Elves]

Yeah, we thought about that, but given the unpredictable nature of the Abyss and the fact that we aren’t going to be given any quarter for a screwup we decided that plane shifting straight in would be a death sentence seeing as the DM could port us in the middle of an entire horde of demons.
If plane shifting in doesn't give you a surprise round, put up contingent celerity (PHB 2) and use it to teleport to safety.

The real problem with Abyss invasions which gets glossed over in every published module is that demons' greater teleport at wills mean an infinite horde can always just descend on the PCs and gib them in the surprise round. Even dimensional lock/AMF only give you a uselessly small radius of safety. You can cast anticipate teleportation and kill them but you'll run out of resources at some point and there are infinite demons. This is why giving monsters at will greater teleportation is kind of dumb and 4e's giving them short range teleportation only is better. As written there's little practical way to succeed unless you can get in completely undetected, then gib him and scram in the same round.

Savage tide just ignores this entirely for some reason but if you want to run this kind of scenario you need to either houserule away demons' teleport or else get realllll high op.

[Satinavian]

Infinite demons theoretically being able to teleport in does not mean they are even aware of your incursion and would bother to do so. I don't remeber demons having any at will communication ability with infinite range and infinite listeners. There will always only be a very limited number of demons who are aware of you until you have moved away again. Most will never know you have ever been there.

[Xervous]

I’m sorry what? Zariel in 3.5e? What kind of nonsense is this?

[paladinofshojo]

I’m sorry what? Zariel in 3.5e? What kind of nonsense is this?

Wait, who’s the leader of the first layer of Baator in 3.5 again? Tiamat? Bel?

[Xervous]

Wait, who’s the leader of the first layer of Baator in 3.5 again? Tiamat? Bel?

Tiamat has her gilded love shack/soul food buffet while Bel is marshaling his forces against the hordes of the abyss

[Peelee]

The Mod on the Silver Mountain: Moved to 3.5

[Biggus]

Knight of the Chalice (CW) and Hellbreaker/Hellreaver (FC2) might be worth a look.

[Max Caysey]

Without going into too much detail I would probably want something like this:

1 Gish Cleric
1 Battlefield Control/ Summoning Wizard
1 Archer (Fighter or Ranger)
1 Crusader/ Paladin (paladins come in all alignments)

EDIT2:If that’s not cheesy enough maybe add mailman sorcerer… or possibly an inspire courage optimized bard. The right build should be able to get close to +15 morale bonus to attack and damage!

It’s more about the jobs the have to do than the actual classes tho.

EDIT1: Also I wanted to comment that if and when doing a campaign like this you should really use Dicefreaks’ write-ups instead of the official ones. They are a lot more interesting and challenging and super well done. At least you should check it out! I believe dicefreaks have made write-ups of all major demon/devil npcs in the game!

[Elves]

Simple Demogorgon strat, no crazy BS

1. Access wish by any of various means and wish for a weirdstone (PGtF). Barring this, take a bunch of your starting WBL in cash and have everyone pitch in to buy one (it's 250k).
2. Make some high Knowledge planes and arcana checks and cast a bunch of divinations. Learn D-dog's whereabouts.
3. Plane shift to plain of infinite portals. Teleport to Broken Reach and buy a tuning fork keyed to Demogorgon's layer.
4. Put up greater spell immunity (blasphemy) at the highest possible CL and any other buffs.
5. Plane shift to Demogorgon's layer. Teleport to his palace or wherever he is currently, as close as you can get.
6. Activate the weirdstone. It turns off teleportation in a 6-mile radius so Demogorgon's armies can't teleport in to help. Its effect projects through solid surfaces, so just put it in a solid container to block LOS/LOE so that it can't be dispelled or disjoined (perhaps an obdurium box with a lid).
7. Kill D-dog's minions, then him. One ubercharge should do it.
8. Deactivate weirdstone and plane shift out.

1.5 (optional). Greater planar ally/bind as many planetars as you can afford.


Edit: Rereading weirdstone, the big problem here is it doesn't stop people from teleporting out of the 6 mile radius, so you need some way to stop Demogorgon from just fleeing.


As for why the angels haven't already done this, it's because it's pointless. Some new head honcho will just arise. You can't really fight a force by killing individuals.

[Tzardok]

Much more important is the question: why haven't the other would-be head honchos of the Abyss not done so already? Orcus, Graz'zt and Obox-ob all want to see Demogorgon dead and wish to replace him.

[GeoffWatson]

Simple Demogorgon strat, no crazy BS

1. Access wish by any of various means and wish for a weirdstone (PGtF). Barring this, take a bunch of your starting WBL in cash and have everyone pitch in to buy one (it's 250k).

It also shuts off SLAs and Su abilities which makes demons easy to defeat and stops them from dispelling it.


For this strat you want to avoid people who use su and sla abilities because the weirdstone shuts them off.

M.

It only stops Su/SLAs that do teleport/divination/etc effects, not all of them.

[TotallyNotEvil]

Without going into too much detail I would probably want something like this:

1 Gish Cleric
1 Battlefield Control/ Summoning Wizard
1 Archer (Fighter or Ranger)
1 Crusader/ Paladin (paladins come in all alignments)

It’s more about the jobs the have to do than the actual classes tho.

EDIT: Also I wanted to comment that if and when doing a campaign like this you should really use Dicefreaks’ write-ups instead of the official ones. They are a lot more interesting and challenging and super well done. At least you should check it out! I believe dicefreaks have made write-ups of all major demon/devil npcs in the game!
Which write ups?

[Anthrowhale]

What sources are available? Dragon Magazine? Settings? Core-only?

For a high power L15 party, I'd make each character a spellcaster with some way to make spells immune to dispelling and persist spells. Once you get caster level up to level 30 or so, you only need to care about disjunction making spells about as robust as magic items, and much more comprehensive/cheap.

[Biggus]

Which write ups?

These were done a long time ago, they vastly increased their CRs. The archdevils were mostly between CR 56 and CR 66, with Asmodeus at CR 81; they were intended for use with a high-epic world (the Dicefreaks 3E campaign setting allowed for characters up to 50th level). I agree with Max Caysey that they're better done than the official ones, but obviously they're only suitable for a high-epic campaign unless you're optimising to the nth degree.

I've got a copy of the pdf they did on archdevils which I'm happy to let anyone have if it doesn't break forum rules (it was given away for free on their website). If anyone has a copy of the demon lords one (or any of their other 3E stuff) I'd be very grateful if they could send it to me (again if it's allowed obviously).

[Max Caysey]

Which write ups?

Dicefreaks! Search Google for dicefreaks gates of hell… there you will find write ups of so many demons and devils, which are more lore accurate than the official!

I weren’t aware they were the old forum stuff published… yeah they are high level tho, but if the lords of hell were only mid 20cr mid level adventurers would kick them around!!

[Biggus]

Dicefreaks! Search Google for dicefreaks gates of hell… there you will find write ups of so many demons and devils, which are more lore accurate than the official!


I did that and there's only stuff about devils there, no demons.

[Max Caysey]

I did that and there's only stuff about devils there, no demons.

Ahh… Sorry! I could have sworn there was both!

My bad!

[Elves]

It only stops Su/SLAs that do teleport/divination/etc effects, not all of them.
Still achieves the main goal -- stop Demogorgon's army from teleporting in on you. Put up a CL-pumped greater spell immunity (blasphemy) and you're good to go.

The only threat is the weirdstone being dispelled. But the unique benefit of a weirdstone is that it explicitly projects through solid surfaces. So just put it in an adamantine cube to block LOS and LOE so that it can't be dispelled or disjoined. Great.


The problem is, now that I reread, the stone doesn't stop creatures from teleporting out of the six-mile radius. So you need to find some way of stopping Demogorgon from fleeing. That becomes the tricky part.


Ahh… Sorry! I could have sworn there was both!

My bad!
I'm assuming we're using the epic level Demogorgon stats from Dragon Mag.

[Max Caysey]

I'm assuming we're using the epic level Demogorgon stats from Dragon Mag.

I wasa unaware that existed. What issue? Gotta check that bad boy out!

[Tzardok]

# 357. One of the last issues of 3.5.

[Biggus]

I wasa unaware that existed. What issue? Gotta check that bad boy out!

They did a fair few of the demon lords in Dragon, generally with higher challenge ratings than the previously published versions. There's a list here: https://forgottenrealms.fandom.com/wiki/Demonomicon_of_Iggwilv_(column)

[Anthrowhale]

I'm still interested in allowed sources---that could matter a great deal. A few possible builds:

Wizard 5/Incantatrix 4/Halrua'an Elder 6 (The last level could be something else.) You have access to circle magic to push your caster level up to 40 and you can make many spells persistent. You can cast 9th level wizard spells by scribing them into your spellbook, heightening some spell with circle magic, and using Rary's Arcane Conversion to convert to the 9th level spell.

Duskblade 1/Wizard 4/Ur-Priest 2/Mystic Theurge 8 You can cast level 9 cleric spells and level 6 wizard spells. Your caster level for Duskblade Spells is 1, wizard spells is 12, and for Ur-Priest is 12. But, using Theurgic Specialist (Dragon#325), it's 25 for every abyssal spell, which includes every evil spell. You can make all spells evil by casting Persistent Touch of the Blackened Soul. And, you can increase your caster level by 10 using Practiced Spellcaster three times.

Wizard 1/Archivist 3/Church Inquisitor 1/Dweomerkeeper 4/Hathran 5/Spelldancer 1. Level 7 divine _or_ wizard spells (via Universal Spirit Magic), which can be heightened to level 20 and caster level 40. Use Spell Mastery[Simulacrum], Uncanny Forethought, and Supernatural Spell to build up a pack of mini-mes for circle magic. The advanced version of this uses an Ice Assassin[Ice Assassin[You]] to avoid having it go berserk and attacking you (use Rary's Arcane Conversion + Circle Magic to access). Spelldancer has a feat tax, but Heroics and/or Mirror Move handle 3 of 4 and Favor of the Martyr handles Endurance. Also qualifies for Initiate of Mystra if you can squeeze it in.

Wizard(Aligned Spellcaster[chaotic](lose familiar), Abyssal Specialist (lose Enchantment?), Spontaneous Divination (lose 5th level feat)) 5/Knight of the Weave 1/Ultimate Magus 9. Caster level for wizard spells is 17 and for KotW spells is 17+1+9=27. With Theurgic Specialist, you then have caster level 44 for nearly all spells. Use Assume Supernatural Ability[Free Metamagic] and polymorph into a Tome Dragon to persist spells using Augmented Casting from Ultimate Magus.

In terms of interesting spells, you might want to persist some always-on free-action attack spells like Lightning Ring or Holy Star with suitable metamagic enancements in addition to various defenses. If the players are working together, they'll use Share Spells via Shapechange or Assume Supernatural Ability+Polymorph to apply each persistent spell to all players in Team Solars style.

[Max Caysey]

I'm still interested in allowed sources---that could matter a great deal. A few possible builds:

Wizard 5/Incantatrix 4/Halrua'an Elder 6 (The last level could be something else.) You have access to circle magic to push your caster level up to 40 and you can make many spells persistent. You can cast 9th level wizard spells by scribing them into your spellbook, heightening some spell with circle magic, and using Rary's Arcane Conversion to convert to the 9th level spell.

Duskblade 1/Wizard 4/Ur-Priest 2/Mystic Theurge 8 You can cast level 9 cleric spells and level 6 wizard spells. Your caster level for Duskblade Spells is 1, wizard spells is 12, and for Ur-Priest is 12. But, using Theurgic Specialist (Dragon#325), it's 25 for every abyssal spell, which includes every evil spell. You can make all spells evil by casting Persistent Touch of the Blackened Soul. And, you can increase your caster level by 10 using Practiced Spellcaster three times.

Wizard 1/Archivist 3/Church Inquisitor 1/Dweomerkeeper 4/Hathran 5/Spelldancer 1. Level 7 divine _or_ wizard spells (via Universal Spirit Magic), which can be heightened to level 20 and caster level 40. Use Spell Mastery[Simulacrum], Uncanny Forethought, and Supernatural Spell to build up a pack of mini-mes for circle magic. The advanced version of this uses an Ice Assassin[Ice Assassin[You]] to avoid having it go berserk and attacking you (use Rary's Arcane Conversion + Circle Magic to access). Spelldancer has a feat tax, but Heroics and/or Mirror Move handle 3 of 4 and Favor of the Martyr handles Endurance. Also qualifies for Initiate of Mystra if you can squeeze it in.

Wizard(Aligned Spellcaster[chaotic](lose familiar), Abyssal Specialist (lose Enchantment?), Spontaneous Divination (lose 5th level feat)) 5/Knight of the Weave 1/Ultimate Magus 9. Caster level for wizard spells is 17 and for KotW spells is 17+1+9=27. With Theurgic Specialist, you then have caster level 44 for nearly all spells. Use Assume Supernatural Ability[Free Metamagic] and polymorph into a Tome Dragon to persist spells using Augmented Casting from Ultimate Magus.

In terms of interesting spells, you might want to persist some always-on free-action attack spells like Lightning Ring or Holy Star with suitable metamagic enancements in addition to various defenses. If the players are working together, they'll use Share Spells via Shapechange or Assume Supernatural Ability+Polymorph to apply each persistent spell to all players in Team Solars style.

Team dollars is a Great place to start looking at optimization ideas. That level of optimization tho is usually not what I would imagine most tables applying but if it fits the campaign go for it!

I still think a well optimized inspire courage bard could be good… especially if not all party members are full casters!

[paladinofshojo]

I'm still interested in allowed sources---that could matter a great deal.

Sorry forgot to mention, all source and supplemental books are allowed! This is a “no quarters given, no quarters asked” campaign…the only “rule” is no egregious homebrew… though “reasonable” homebrew is allowed.

This DM is the type of person who likes to have sadistic “challenge mode” games where he gives an already powerful party a pretty Herculean task and throws the most overpowered bull**** against us. This whole game is basically just a challenge, “kill Demogorgon” and we win. Even if our characters end up dying from their wounds afterwards, the campaign is a success if we take the big D down with us.

Our last campaign was to slay Tiamat, which we had done by launching a total and complete genocide against all chromatic dragons in Faerun to weaken her and by negotiating a deal with Asmodeus involving the souls of the party offered to him in exchange for no infernal aid to the Dragon Queen.

Basically, our GM is going to punish us for every tiny mistake, and will probably include sadistic traps and mechanics that will be just as broken as anything we can come up with.

This is why we are hesitant with just plane-shifting into the Abyss, because we know it’s going to be a death sentence with us ending up in the circle of infinite demons if we are lucky. So we are currently trying to figure out what’s the strongest, most broken party comp we can make with 5 adventurers at the 15th level.

[Elves]

This is why we are hesitant with just plane-shifting into the Abyss, because we know it’s going to be a death sentence with us ending up in the circle of infinite demons if we are lucky. So we are currently trying to figure out what’s the strongest, most broken party comp we can make with 5 adventurers at the 15th level.
First question is why is Demogorgon going to stick around to get murked? Have to draw him out somehow or get really good at stealth.

Nothing can fight t-op characters except other t-op characters, so I don't think that's the route to go. Demogorgon and the high level demons are at the power level where any decently optimized char works, the main challenge is just covering your ass.

[Anthrowhale]

Of the builds mentioned, the IoM one seems particularly compelling because demons are mostly scary due to SLAs & Su abilities.

So, maybe a good goal for a single character is the party persistomancer? Consider:
LG or LN Human Archivist 1/Wizard 1/Archivist 2/Church Inquisitor 1/Dweomerkeeper 4/Hathran 5/Spelldancer 1.
Feats:
Human: Ethran
1. Extend Spell
Archivist 1: Scribe Scroll
Wizard 1: Use Martial Wizard to get Improved Initiative... or any other preferred fighter feat.
3. Spell Mastery
6. Leadership
9. Uncanny Forethought
12. Persistent Spell
15. Initiate of Mystra

Unobvious requirement satisfaction:
Initiate of Mystra: qualify with 3 levels of Hathran (which requires worshipping a deity) which advances Archivist which uses the cleric spell list as per the modification to requirements in Dragon Magic.
Dweomerkeeper: Use Substitute Domain[Magic]
Circle Magic: Use Spell Mastery[Simulacrum] for a scribed scroll of Simulacrum in your spellbook. Heighten an L1 Wizard spell to L7, then use Universal Spirit Magic to cast Rary's Arcane Conversion to convert the L1 Wizard Spell into a Simulacrum. Cast Simulacrum using Supernatural Spell. This gives you a zero cost Simulacrum which can provide level 3 spells for circle magic purposes.
Spelldancer 1: Use Circle Magic to heighten a L1 wizard spell to L9, then use Universal Spirit Magic off of an Archivist L6 spell to convert the L9 wizard spell into Extended Persistent Mirror Move (http://web.archive.org/web/20161101181035/archive.wizards.com/dnd/article.asp?x=dnd/sb/sb20000901a) to pick up Combat Casting, Dodge, and Mobility. Use (Persistent) Favor of the Martyr to pick up Endurance.
Antimagic Fields & your personal Supernatural Abilities: You may need to cast AMF before using Spelldancing or other supernatural abilities. To do that, cast AMF and then Greater Polymorph[Sun Giant] to become Huge. Note that Polymorph is in the Transformation domain, so you can learn it as an archivist. Part of you (you choose which part) must poke out of the AMF enabling the use of Su Abilities.
Persistent party: Everyone can benefit from your persistent spells via Polymorph into a symbiote from Fiend Folio and Assume Supernatural Ability[Share Spells] (which other party members must take). Stick the Symbiotes on the part of you which extends out of the AMF.
Keeping Simulacrums safe: store them in a portable hole or similar, and only let them out in a safe space like Mord's Mansion (which, yes, is a 7th level spell on a domain list, so you can cast it directly off of archivist slots).
Circle Magic mastery: Time is the only limit on the number of times/day you can use Circle Magic.

At this point, you can persist a large number of spells for the whole party every day at caster level 40 which work inside of antimagic field. Even 10 minutes/level spells last for a full adventuring day when extended. This includes Antimagic Field, so any party member who wants to (they have to give up magic items) can benefit. It also includes Arcane L5- spells via Greater Anyspell.

For example, using Extended Persistent Draconic Polymorph[War Troll], Extended Persistent Wraithstrike, Extended Persistent Divine Power, Extended Heroics[Power Attack], Extended Persistent Flight of the Dragon, and extended persistent AMF, you can engage in demon slaughter for an indefinite time period.

There are a few other elements to consider:
(1) How do you get there? You could use 2 7th level slots to Greater Planeshift in and make progress each day then Greater Planeshift back to somewhere safe.
(2) How do you kill it? Surge of Fortune + Sense Weakness + a Vorpal Weapon would kill it in 2 hits, but you'll have to dismiss AMF to apply. Alternatively, lots of damage could work. On the spell side a mailman focusing on (Searing Spell fire damage or Planar spellcaster force-charged magic) could be powerful. On the Melee side, an ubercharger could have a moment to shine. Either way, you must either win initiative and get it done or pin it down. The best pin down combo might be a high caster level dimensional lock + forcecage.
(3) Keep it dead? Maybe use a Thinuan blade. Maybe try a Supernatural Heightened Unname.

I also agree with the comments about stealth. You need either stealth or deception to get in position to execute.