(3.5) monster progression+Caster level?

[lrellok]

Several monsters have caster levels both for spell like abilities and for actual spell casting (naga hydra is the one i am working on). However, the Monster manual section on advancing monsters via HD does not cover how to advance their caster or spell levels. Does anyone know where this info might be found?

Specifically, if i advance a monster from 18 HD to 54 HD, and it was caster level 15, how much does its CL go up, if at all??

[Belial_the_Leveler]

Generally speaking, caster level should advance by CR, not HD.

[Irreverent Fool]

Advancing a monster's HD by monster-type (humanoid, monstrous humanoid, elemental, etc) doesn't improve its spellcasting unless that advancement specifically says so.

If a monster casts spells as a sorcerer of X level, then in order to advance that spellcasting, the monster must take levels in that class.

From Improving Monsters/Adding Class Levels:

A spellcasting class is an associated class for a creature that already has the ability to cast spells as a character of the class in question, since the monster’s levels in the spellcasting class stack with its innate spellcasting ability

Generally, this means that if you want to advance a creature's spellcasting, the creature should have 'by character class' in its 'advancement' entry, such as the Rakshasa, though as a DM you can always fudge a bit.

I can't find anything in the Monster Manual either. It's so much easier when you can do a 'find on page' for 'spellcasting' in the SRD.

In what book is this naga hydra you're advancing?

obnoxious
sig

[Biffoniacus_Furiou]

Some monsters specifically cast spells as a [class] of their [(racial) HD +X]. For example, there's the Spellweaver in MM2, which casts spells as a sorcerer two levels higher than its Hit Dice. Other monsters just cast spells at a set level, such as an Aranea, a Lammasu, and true Dragons. For those creatures, advancing their racial hit dice won't advance their spellcasting, but you can give them levels in that spellcasting class or in a prestige class that advances spellcasting to further improve it. In the case of dragons, their spellcasting increases to a new set level at each new age category, but adding one or two additional hit dice without increasing their age category will not improve their spellcasting ability.

In the case of advancing a monster to an extremely high number of HD, consider including five Abjurant Champion levels, from Complete Mage. That will give them +5 levels of spellcasting ability, and their caster level for all spells will be equal to their base attack bonus. For an Aberration, every associated class level increases its CR by the same amount as an extra 4 HD, so you'd end up at 34 HD of Aberration and 5 levels in Abjurant Champion for the same CR, but its caster level would be at 30, possibly even 34 with Practiced Spellcaster. Plus it would get the elite array for no additional CR due to having class levels. If it started as a 15th level spellcaster, it would have 20th level spellcasting ability, which it wouldn't need any more of anyway.