How much do you advance the caster level when you advance a monster?

[Vahktang]

So, the monster has spell like abilities.
When you up the HD, upping the CR, how much do you up the caster level?
One for one? By HD or CR?

For example, a guardian naga, 10 HD, 9th level caster, CR 10.
(Forgive me if it is not exact, don't have the books with me)
It's an abberrition (sp) so you up it 4 HD for 1 CR.

It's now 14 HD.
So, is it now 13th level caster, one less than the HD, as before?
10th level caster, one less than the CR, as before?

And what about advancing Magic Resistance?
Is that 1 pt/HD? Or what? A ratio?

Any insight would be appreciated.
Thanks.

More later,

Vahktang

 

[Garnfellow]

So, the monster has spell like abilities.
When you up the HD, upping the CR, how much do you up the caster level?
One for one? By HD or CR?

By the Rules As Written, advancing a monster does not increase caster level or SR unless the monster description specifically says so -- for example, the drow.

(The Monster Manual II, in its example of advancing a monster, increases the SR +1 by every +1 CR. But this rule is never explicitly called out there, never mentioned in Savage Species, and was not added in to the 3.5 rules for monster advancement, so I think this must be considered unofficial.)

All that said, I don't think it hurts anything to increase SR and caster level by +1 for every +1 increase in Challenge Rating as a house rule.

 

[Hypersmurf]

By the Rules As Written, advancing a monster does not increase caster level or SR unless the monster description specifically says so...

Or unless the caster level is unlisted, in which case it is equal to hit dice... so when a monster with an unlisted caster level increases in hit dice, its caster level increases...

For creatures with spell-like abilities, a designated caster level defines how difficult it is to dispel their spell-like effects and to define any level-dependent variables (such as range and duration) the abilities might have. The creature’s caster level never affects which spell-like abilities the creature has; sometimes the given caster level is lower than the level a spellcasting character would need to cast the spell of the same name. If no caster level is specified, the caster level is equal to the creature’s Hit Dice.

and

Unless otherwise noted, a supernatural ability has an effective caster level equal to the creature’s Hit Dice.

-Hyp.

 

[the Jester]

By the RAW, you don't, but it's all too easy to end up with a CR 20 monster with a CL of 8 and SR 20 that way. I wing it if I feel it's necessary to increase CL, SR, DR, damage from special attacks or what have you. Notice that some of the advanced monsters in the 3.5 MM also have a few unexpected boosts like this- iirc, the advanced hell hound's breath weapon is higher damage, for instance.

 

[Gez]

Personally, caster level for my monsters is always based on HD. HD/2 for dragons (who have lots of HD), HD for fey, and so on.

 

[Shellman]

By the Rules As Written, advancing a monster does not increase caster level or SR unless the monster description specifically says so -- for example, the drow.

(The Monster Manual II, in its example of advancing a monster, increases the SR +1 by every +1 CR. But this rule is never explicitly called out there, never mentioned in Savage Species, and was not added in to the 3.5 rules for monster advancement, so I think this must be considered unofficial.)

All that said, I don't think it hurts anything to increase SR and caster level by +1 for every +1 increase in Challenge Rating as a house rule.

Garnfellow and Hypersmurf are correct,

Caster Level does not increase when you increase the CR. There is nothing written to indicate so. There has been a lot of Savage Species content changed since its publication, so it would be advisable to check newer publications for updated content.

I wish there was, I am playing a Warden Archon in a game now and it would be a great help if my caster level could be advanced. My DM has ruled that unless the creature description states the caster level increases with your HD, then the caster level is fixed for those spell-like abilites regardless of any increase in CR in the future.