How can I tell how many HD an enemy has?

[erok0809]

How would I go about figuring out how many HD an enemy has? A warmage boss of mine is going to have the spell "Circle of Death" which can only affect creatures up to 9 HD. How would he go about learning how many HD an enemy has, to make sure of whether or not they have over or under 9 HD? Or would he just have to try it and hope it works? Could I use some sort of Knowledge check?

[Flashy]

It depends how metagamey you want to be. In game his understanding would essentially be that the spell only kills the weak, and he'd probably have a fairly useful working definition of weak. While he wouldn't know for certain that a Chimera would be immune while a Gynosphinx wouldn't he'd certainly be able to guess that an owlbear would succumb, but not a great wyrm. Give him a reasonable degree of understanding and don't worry about the specifics too much unless you have to. If you feel he'd absolutely not use it without knowing for sure it'd work I'd probably rule it as a knowledge: relevant animal identification skill check with a DC in the low 20s, since "Does this one specific spell work on this particular creature" is pretty obscure.

[Taveena]

According to the spell Trap The Soul, hit dice can be researched in-character.

It gives no method of doing so.

[Hand_of_Vecna]

There's the new use for Sense Motive in Oriental Adventures. Of course wether it works outside Rokugan is up to the DM and they may be iclined against it, because the listed DC's are quite low. The mechanical ability is pretty necessary in that setting, since one on one fights to the death are an inherent part of the setting.

[Silva Stormrage]

With power sight from Master's of the Wild. Essentially all it does is grant you the ability to see an opponent's HD. Try getting a custom continuous item of it if your DM likes custom items.

[BloodyMartian]

Pg 102 of Complete Adventurer gives a use of Sense Motive.

[DeltaEmil]

Pg 102 of Complete Adventurer gives a use of Sense Motive.That one's about assessing an opponent's Challenge Rating.

[BloodyMartian]

Could've sworn it was HD. My bad.

[Psyren]

According to the spell Trap The Soul, hit dice can be researched in-character.

It gives no method of doing so.

You could use the Truename research method from ToM - that should be able to determine HD too.

[Miss Disaster]

I believe the Urbant Savant PrC in Cityscape has a class feature that can determine enemy HD. It's a PrC for all arcane spell casters.

[Fitz10019]

Meta: Pretend you've miscalculated your knowledge check, increasing by one each time, until the DM tells you a useful bit of knowledge about the monster, then subtract 10. Heh.

Non-meta: I would allow the question, "is it hardier than a chimera against Circle of Death?" with a 10+HD+5 on the appropriate Knowledge check.

[Kennisiou]

So as a GM I'd say...

Oriental Adventures can allow you to sense motive to figure out what class levels something has. A good roll of the proper knowledge skills shows the standard amount of RHD something has. A high enough gather information or appropriate knowledge check made well beforehand could give you that kind of information about someone famous.

By RAW, only the first one actually works though.

[erok0809]

Alright, thanks for all the answers. I am the DM in this case, I just wanted to see if there was a RAW way to do it before I went and made something up myself. I'll probably use the sense motive from Complete Adventurer, since the PC he's going to be fighting (solo campaign) would have a "CR" of his class levels for the warmage. That makes the most sense anyway, where he would know, relative to himself (he's level 12) that the fight would have to be a "Pushover" for him to confidently use Circle of Death. So if he can win the Sense Motive roll, he won't use it, since the PC is not a pushover. If he fails it, he'll probably use it, making the assumption that the PC is weak, because he's an arrogant jerk. Thanks guys!