I'm running a high level campaign that's a mix of homebrew and FGG's Rapan Athuk, and my PC's are embroiled in an interplanar conflict between the Four Horsemen of the Apocalypse, and the long lost "Fifth" Horseman (The creator of all demon kind). There's at least a word doc page of backstory that I'd have to run through to make it all make sense, so you'll just have to go with me here. The long and short of it is that the fifth horseman was split into pieces and trapped in 6 different weapons. Four of these weapons are broken and released their power back to the main weapon, and a fifth one is in possession of the party, and the sixth is the god sword. I need some epic mooks for the final showdown between the PC's and the poor sod that picked up the bastard sword and is now a vessel of this mad god.
The PC's are around 19-20, and for the most part well optimized. The one thing they lack is a dedicated Arcane caster, though they have a Magus who helps fill that roll. The BBEG is a 20th level Invulnerable Rager who is stat-stacked out his ears, and has two templates (Fiendish and Broken soul). Adding to his CR is the magic weapon, which has the casting of a level 17 cleric, and gets it's own standard and swift action every time the barbarian takes his turn. Due to this massive action economy advantage, I estimate he alone is about a CR 25, and they're going to end up fighting him twice in succession (the sword prepared Resurrection).
Be creative! Thanks!