Would you please estimate the CR of this Aspect of Lolth

[Shin Okada]

Aspect of Lolth (Miniatures Handbook) is a relatively simple melee monster with 14 outsider HDs, DR 5/Epic, SR 25 & only one poisonous bite attack at +18.

Now I am bumping her up to 18HDs, make her huge, and let she cast spells as a 18th-level cleric. The rough result will be,

AC 23 (touch 11, flat-footed 20)
hp 189
DR 5/Epic
SR 29
Save F+17, Ref+14, Will +19
Bite +24 (2d6+12/19-20 and poison)
Str 24, Dex 16, Con 22, Wis 26, Cha 23

With casting ability as a 18th-level cleric, how much should be the CR of this monster? 18? 19? or maybe 20?

Opinions are welcomed.

 

[Grogg of the North]

Well, by advancing HD she would only get +2 CR (+1 per 2 HD). I think you could add another +1 for a size increase. So original CR+3?

Does her SR and spell casting advance as well or is it pegged at 25 and a specific level?

 

[Shin Okada]

Well, by advancing HD she would only get +2 CR (+1 per 2 HD). I think you could add another +1 for a size increase. So original CR+3?

Does her SR and spell casting advance as well or is it pegged at 25 and a specific level?

The original Aspect of Lolth is only CR 11 as she is just a simple melee monster and does not cast spells nor has spell-like ability. In regard to SR, I have increased her SR to 29 as I have advanced her by 4HDs.

 

[Celebrim]

CR 17ish

The casting ability doesn't add a whole lot to the CR or conversely the other abilities don't add a whole lot to the casting ability. If she's in melee, she's not going to get off a lot of spells successfully. If she's not in melee, then she's just a cleric without a bunch of gear - and cleric is itself a second line support class that is mainly useful for bolstering allies. A lot of clerical tricks to turn them into combat tanks aren't going to help much since she's already a huge outsider. If she has time to prepare Divine Favor, Bull's Strength, and so forth, it will boost the CR a bit - but that's mostly what she'd get out of spellcasting. The big worry of course is that she could get far away enough to get a Heal off late in a combat, but ultimately that sort of pure defensive strategy is just prolonging the fight and probably not changing the outcome.

So we are dealing with a really what is just a Cleric with some unusual gear and a really bad AC. You could of course put the Aspect in a situation that greatly favors it and lets the Aspect get off more offensive spells in a more potent way, but that would be one of those situations where you award 200% normal XP owing to the unfavorable circumstances of the fight - not something that proved it had a higher CR.