Imaginary Number
First Post
I think I'd make a distinction between npcs that are intended primarily to be antagonists for the players in the context of a specific adventure and npcs that are intended to play a larger role in the campaign world/storyline/whatever. For npcs in the former category, I agree that they should be treated like any other monster, which means that they should be beatable. Twinking out an NPC to make it practically unhittable will do nothing more than lead to frustrated players. For npcs with a larger role in the campaign, I also agree with those who have mentioned that the npc's role will dictate how powerful they are and how difficult they are to defeat: the king's champion likely will have a higher AC than the local captain of the guard, for example, who in turn likely will have a higher AC than the local peasant farmers.