Psion said:
I am not sure how close it is to the monster section, but there is also mention elsewhere in that chapter about using the PC rules for "special" NPCs.
And WotC does it in the modules.
And if that's not justification enough for you, there is always rule 0. But I was sort of avoiding that, because lots of people act like once rule zero is mentioned, anything that follows has no bearing.
But really people, trust me: No matter how technically correct you think it is, adding class levels to fiends makes them more interesting and challenging.
If you want to scare a party, put them in a fight with a a few dozen 2 to 3 hit dice creatures that are resistant to most elements. THAT will unnerve a party, unless they are 15th to 20th level. Why? Sheer numbers of attacks. Player Characters do this all the time. If one side has a horde of lower level enemies against one high-level one, the horde always wins. So just make sure you're the one with the horde.
One thing so many people forget about demons: Coming from the Abyss (or wherever the come from in your cosmology), they are not necessarily in one set form. Old Dragon Magazines used to have random tables to generate the features, appendages, hit dice, attacks and damage, etc. etc. etc. of random Demons. Why subject your PC's to an old enemy when you can face them with dozens of demons, no two of which look alike? You can give them the SAME stats, but the players don't need to know that. They will likely treat each type as a different demon. And THAT is worth the fun a player has when faced with the unknown.
Also, don't forget vivid description. Paint a very real mental picture of dozens of large, animalistic, slavering, smelly, puke-colored, dog-headed, fish-eyed, scaled, feathered, crowing terrors rushing directly at you, and see if the players take notice more. Describe to them every vivid detail - and when their mass-damage elemental spells have little effect on them, watch them switch tactics, and later tell you how much fun the encounter was.
When a ball-game is in a rut, the Coach puts in another pitcher to shake things up a bit. You can do the same. When the "players" realize you, "their coach" are not making wrote plays out of the "handbooks", they look at you with a new respect.
