How did other people handle him? What I don’t want to do is have him use all his most potent abilities since, if I was Kaurphon, I wouldn’t bank on the party resting (and know my party they always push themselves until not only have they run out of all spells but everyone is low on hps) at the end game (3rd test). But he does need to help just to build up the parties trust.
The other issue I have is that whenever I have an NPC join the group (summons, temp allies, Alek etc) I have the party run the NPC in combat. However I don’t want to give them the full stats otherwise they will get an inkling of what’s going on. But if I don’t give them something they will automatically becomes suspicious.
So I was going to give them a “lower level” kaurphon with some of his spells missing (like Cone of Cold which he will keep in reserve) and none of his personal information there (like smite good, alignment, race etc).
I also noticed some things were wrong with his stats (even in the HC). He is CR15 not 14, he has no familiar (I assume this is on purpose) and is missing a feat. Because his ECL is 15 his cone of cold does a minimum of 15d6 (not including caster bonuses from the fountain of evil). I was going to give him a vile feat or improved familiar and something useful to use – like an imp or evil wyrmling.
I think the party will be suspicious no matter what you do. It's what we like to call good old fashioned PC paranoia. If you do give your party Kaurophon's stats, make sure you can explain some of the alterations. For example, if you change his alignment to CG, make sure he has an item to mask his true alignment (e.g. a ring of undetectable alignment). And also make sure that item either has some other purpose (e.g. disguised as a ring of protection). Otherwise, pc's will catch on to his ruse in no time.
I'll just be blanking out that info so they don't see it. And knowing my players they won't ask or attempt to detect alignment. At first anyway.
How did you go with the nexus of evil part? I can't really see the advantage for Kaurophon touching the nexus and losing levels for a spell bonus for 1hr. Unless he *knows* the cleric will restore him. Which might be iffy.
Guess will have to call it at the time.