How can I best optimize an NPC so that instead of having perfect power attack or sneak attack, they're just really hard to kill? I can think of thief acrobat and perhaps exemplar or dungeon delver, but not too many others. Strangely. I never really looked for ways to make a non- or minimal-combat NPC just for the sake of surviving to either torment or simply antagonize the PCs.
I've read about ghosts and the jester taunt whatchamacallit, but I'm curious if anyone has or would know how to best make a living humanoid nigh-impossible-to-destroy creature?
PC levels, I'd like them to not be able to be rid of this creature until epic level but at the least eighteenth level. I'd like this creature to be between thirteenth and sixteenth level but will fold for as high as eighteen. No specific setting in play currently, just my homebrew which has severe restrictions on interplanar travel but that's about it. Allowed books are all core, Complete Warrior, Complete Adventurer, Book of Vile Darkness, Complete Arcane, and all open source stuff from Unearthed Arcana and the Psionics Handbook. Any race from core or open source books, ideally a low level adjustment (less than four with HD included). Human, elf, gnome, goblin, bugbear, halfling, troglodyte, lizardfolk -- you get the idea, something semi-common and not very powerful at base.
Noted exception - if one can make this with a lycan build, then that would be allowable as there's a big focus on lycanthropy in the campaign world.
Alignment isn't a constraint, because even a lawful good NPC can become a thorn in the PCs side through the course of this campaign. I don't have a role cut out for them, wanted to make them before I decided how they affect plot.
So far the party comprises of a prestige bard/dual wielding specialist, a mounted combat focused scout/prestige paladin, a ranged-and-spell specialist prestige ranger/druid, and some sort of roguey good guy will join them down the line (as-of-yet unfleshed NPC). However, another character is running an information guild (think COINTELPRO from the late sixties) and is a ninja type with an emphasis on disguise and roleplaying elements, along with surprise combat. I'd like for the classes to do the job the best, but I know I'll need to put in some magic items to supplement them. Just want to be minimal on the latter.