I was flipping through Unnapproachable East, the supplement for Forgotten Realms and passed over the Black Flame Zealot. Its a very interesting prestige class which lends itself very well to villains.
Consider:
Human Rog3/Ftr4/Assasin3/Blackguard3/Black Flame Zealot7
BAB: +16
Sneak: +6d6
Death Attack: 20+Int
Spells: As 3rd level Assasin and 6th level Blackguard
Saves: 11/13/9
The only problems are the confining feats necessary to be a blackguard. I think the best path may be a dual-wielder with longsword and kukri, but you don't have enough feats to concentrate on both weapons, so I say focus on kukri. Giving the villain an Adamantium Keen Shatterspike +1 and a Human-Bane Vorpal Kukri +1 makes for an interesting set of weapons, especially as most will assume that the longsword is the threat, especially as it will be under the effects of the Sacred Flame ability. Have a couple priests who can cast Greater Magic Weapon to ensure his weapons aren't too easy to break, and he will be ready to go.
For feats get all the 2wf, WF, WS, and Imp Crit for Kukri. Pick up everything thats required for the 3 prcs and pick up some general rogue skills.
Along with a few flunkies to help give sneak attack, this seems like it would present a very good CR 20 challenge. The trick is, of course, using blackguard to get divine spells level 2 instead of taking 3 levels of cleric (which still isnt a bad idea, I just think the blackguard works better abilities-wise). If you are feeling especially devious allow the Assasin levels to advance the blackguard progression (instead of its own list) and change the fighter levels for paladin levels (in order to trade them in for blackguard abilities - but this may require dropping TWF).
Technik
Consider:
Human Rog3/Ftr4/Assasin3/Blackguard3/Black Flame Zealot7
BAB: +16
Sneak: +6d6
Death Attack: 20+Int
Spells: As 3rd level Assasin and 6th level Blackguard
Saves: 11/13/9
The only problems are the confining feats necessary to be a blackguard. I think the best path may be a dual-wielder with longsword and kukri, but you don't have enough feats to concentrate on both weapons, so I say focus on kukri. Giving the villain an Adamantium Keen Shatterspike +1 and a Human-Bane Vorpal Kukri +1 makes for an interesting set of weapons, especially as most will assume that the longsword is the threat, especially as it will be under the effects of the Sacred Flame ability. Have a couple priests who can cast Greater Magic Weapon to ensure his weapons aren't too easy to break, and he will be ready to go.
For feats get all the 2wf, WF, WS, and Imp Crit for Kukri. Pick up everything thats required for the 3 prcs and pick up some general rogue skills.
Along with a few flunkies to help give sneak attack, this seems like it would present a very good CR 20 challenge. The trick is, of course, using blackguard to get divine spells level 2 instead of taking 3 levels of cleric (which still isnt a bad idea, I just think the blackguard works better abilities-wise). If you are feeling especially devious allow the Assasin levels to advance the blackguard progression (instead of its own list) and change the fighter levels for paladin levels (in order to trade them in for blackguard abilities - but this may require dropping TWF).
Technik
