So, I have a character who has just made a bargain with a powerful being (who is NOT a friend) to be Resurrected into a new, more powerful form. (aka, he wanted to switch from Bard to Magus while retaining character continuity, instead of just making a new character.)
He's a black-blade magus, and I was thinking maybe rather than a normal black-blade, this one is actually powered by a part of the soul of a fallen employer (a relatively affable* lich whom the characters liked a lot). Between the two of them, they have NG vs NE personalities, but they share a lot of the same goals. They both want to kill the guy who was responsible for said resurrection.
I was thinking this show itself as a sort of berserk-mode where, when, some time later when he's in danger**, the special powers of the sword (randomly rolled at will-sixth level spell for the intelligent item power.. It was a very good roll) the lich temporarily takes over with lots of black aura rawr stuff.
Later on he can figure out whether he wants to negotiate with the lich's soul, or coexist, or find a way to exert dominance (ego rules or whatnot), or purge him.
What do you guys think? I think it would be kinda epic and the player might enjoy it, but on the other hand, taking control out of the players hands, even temporarily, is VERY dangerous. And having an intelligent sword that has dramatic alignment differences as a class feature might just be too annoying. On the flipside, if it's too easy for the player to get that power boost at no downside, the other players might feel the player well, got a free power boost.
*but still quite evil
**as in "oh crap, I'm under 20 hp with no defensive/escape abilities left" sort of danger, not everyday adventurer danger.