Monstrous spellcaster

[CIDE]

Ahoy-hoy Playground,

In a theoretical optimization scenario let's say a player character, villain, or whoever is altering and/or building a monster from existing monsters. Whether through Pun-pun shenanigans, Wish abuse, rituals, or however else they're trying to build but without the ability to confer class levels onto the monster how crazy could we get with spellcasting?

We'll say for the sake of simplicity it's arcane only, a single spellcasting pool, and while they can exceed CL 20 they don't get access to epic level spells. Could any monster special ability or spellcasting even stack with other monster entries as per RAW? Bonus points for getting the highest CL or spell level with a lower CR/HD.

Some obvious starts are Spellweaver or Phaerimm. Anything else that works?

[Anthrowhale]

You could perhaps drain a Black Ethergaunt to level 1 and then pick up 16 (or 17 with buyoff) levels of wizard that stacks with racial casting resulting in an effective level 33(or 34) wizard.

[Asmotherion]

I think the easyest solution is through PaO.

Other than that, an other interesting solution is with Create Undead to make a Bone/Corpse creature. They keep their spellcasting.

[Beni-Kujaku]

Ahoy-hoy Playground,

In a theoretical optimization scenario let's say a player character, villain, or whoever is altering and/or building a monster from existing monsters. Whether through Pun-pun shenanigans, Wish abuse, rituals, or however else they're trying to build but without the ability to confer class levels onto the monster how crazy could we get with spellcasting?

We'll say for the sake of simplicity it's arcane only, a single spellcasting pool, and while they can exceed CL 20 they don't get access to epic level spells. Could any monster special ability or spellcasting even stack with other monster entries as per RAW? Bonus points for getting the highest CL or spell level with a lower CR/HD.

Some obvious starts are Spellweaver or Phaerimm. Anything else that works?

Something easy to do would be to take a Spellweaver, increase its size permanently, then apply multiheaded template. Not only each new head increases the number of racial hit dice, but it also qualifies it for Multivoice, doubling its number of spells per round.

If you have ways to increase the monster's RHD to arbitrary levels (one good way for that is to make it a Lycanthrope of an arbitrarily high HD Animal), the Sylph is even better than the Spellweaver, since her CL is equal to her RHD+4. For example, a max-advanced, max-multiheaded Dire were-elephant Sylph has a colossal, 45+12+2x29=115 RHD animal form, and 119th level sorcerer casting.

[Metastachydium]

Something easy to do would be to take a Spellweaver, increase its size permanently, then apply multiheaded template. Not only each new head increases the number of racial hit dice, but it also qualifies it for Multivoice, doubling its number of spells per round.

If you have ways to increase the monster's RHD to arbitrary levels (one good way for that is to make it a Lycanthrope of an arbitrarily high HD Animal), the Sylph is even better than the Spellweaver, since her CL is equal to her RHD+4. For example, a max-advanced, max-multiheaded Dire were-elephant Sylph has a colossal, 45+12+2x29=115 RHD animal form, and 119th level sorcerer casting.

Unless that dire elephant is Medium-sized and unless it CRAVES THE FLESH OF MORTALS, I'm not sure that's possible („[t]his animal can be any predator, scavenger, or omnivore whose size is within one size category of the base creature’s size (Small, Medium, or Large for a Medium base creature) (https://www.d20srd.org/srd/monsters/lycanthrope.htm)”).

[Beni-Kujaku]

Unless that dire elephant is Medium-sized and unless it CRAVES THE FLESH OF MORTALS, I'm not sure that's possible („[t]his animal can be any predator, scavenger, or omnivore whose size is within one size category of the base creature’s size (Small, Medium, or Large for a Medium base creature) (https://www.d20srd.org/srd/monsters/lycanthrope.htm)”).

That is no real problem. Double Polymorph any Object into an Ibrandlin (10 HD, Gargantuan, yes, you have 4 Int, but you keep your Cha, so no problem), then get bitten by a colossal were-Monstrous Spider with 30 heads and 118 HD. You are now enthomanothrope (https://www.realmshelps.net/monsters/templates/bugs.shtml)! Congrats! And you have a lot more problem to fit in society, but that's not what we're here for. We're here for the sweet sweet lv 134 sorcerer casting.

[Gruftzwerg]

Symbiotic (Template) + Warlock/DFA invocations (+ Ice Assassins)

The Symbiotic template lets a "guest" character become a +1 template for a "host" creature. The host gets all the mental and special abilities of the guest. This includes all invocations (SLA). This is where the warlock/dfa comes into play. Finally use Ice Assassins of yourself as "guest" to enhance your monster army.

Have a look at my Orochimaru build (see signature) who abuses this combo to the fullest. Look at the Curse Mark related stuff there.

[Beni-Kujaku]

Symbiotic (Template) + Warlock/DFA invocations (+ Ice Assassins)

The Symbiotic template lets a "guest" character become a +1 template for a "host" creature. The host gets all the mental and special abilities of the guest. This includes all invocations (SLA). This is where the warlock/dfa comes into play. Finally use Ice Assassins of yourself as "guest" to enhance your monster army.

Have a look at my Orochimaru build (see signature) who abuses this combo to the fullest. Look at the Curse Mark related stuff there.

I'm not sure having a Symbiot with class levels counts as not having levels. Also, I think they wanted a spellcaster-type monster, more than an invocation-user. But your Orochimaru build is incredible, the level of cheese is almost mind-bogglingly high, and that's hilarious.

[Gruftzwerg]

I'm not sure having a Symbiot with class levels counts as not having levels. Also, I think they wanted a spellcaster-type monster, more than an invocation-user. But your Orochimaru build is incredible, the level of cheese is almost mind-bogglingly high, and that's hilarious.

My point is that the class level don't carry over via the symbiotic template. But the SLA do. You are just limited to those that work without casterlevel (since those are tied to the class level that the host doesn't get). Imho a cheesy but legal entry here.

And yeah, Orochimaru is not really meant for play and thus is marked as pure TO (theoretical optimization). As said in the build: It reads more like an entry in a contest for "most cheese in a lvl 20 build" but what do you expect if you try to adopt Orochimaru into 3.5 (the most game breaking system ever imho).

Since the OP also asked for "Pun-pun shenanigans" level of solutions, this is what he got in return xD

[Thurbane]

As well as Mutliheaded, another way to add HD to monsters that advance casting by HD (Spell Weaver, Sylph) is to apply the Half-Giant Troll template, then have them afflicted with lycanthropy or entamanothropy.

A Half-Troll Sylph Were Legendary Wolf, assuming 3 Sylph HD, will have a Sorcerer level of 21, and a CR of 12. You may want to do something about the hit to Cha, though.

[Particle_Man]

Dragons get more spellcasting ability as they get into higher age categories, so perhaps something can be done with that. I mean a Great Wyrm Gold Dragon has sorcerer caster level 19 (with access to cleric spells, law, luck and good domains as known spells) right out of the MM or SRD. So that is 9th level spells right there. And they are a dragon. A really big one. Claws, teeth, wings, breath weapon, SR, etc.

[ShurikVch]

The best templates for HD-based spellcasting are:
Forestmaster (Bestiary Of Krynn, Revised): as Druid
Half-Titan (Bastards & Bloodlines): as Cleric or Wizard
Ogre Mage (Horde Player's Guide): as specific Arcanist or Healer path (World of Warcraft: The Role-Playing Game) with few specific spells always known
Psionic Creature (Psionics Handbook): picks few Psion powers (usable at will); power's level is up to HD+2

For the extra HD - how about the Kaiju template (Dragon #289)? +40 HD...

[Psyren]

Pathfinder has simple class templates (https://www.d20pfsrd.com/bestiary/monster-listings/templates/simple-class-templates/) that you can quickly and thematically bolt onto various monsters, e.g. giving a treant or dryad some druid spellcasting that roughly aligns with their CR without having to go through all the effort of adding class levels to them manually. The source of these is left intentionally vague - divine intervention, magical anomalies, or even special training undertaken by/imparted onto the creature. You can use the core templates as a guideline to create similar templates for other classes, e.g. making a Pixie Beguiler or a Bariaur Healer.