Crothian said:
Well, it is by no means original, this has been discussed before in different ways. I agree let him have his fun, but their are consequances for his action. You shouldn't let him kill have a village and not have anyone notice or care. An army of shadows is going to attract attention. And if the DM rules when he stops being a shadow he loses control of theml; then that's fine to. People really aren't trying to screw him, they are just figureing out how it would logically play out by the rules.
Nothing's original, if you want it that way. Every single idea, ever, has been discussed endlessly in countless boards just like this one. But it is reasonably novel, especially if he came up with it himself. Having paladins chasing after him for this is fine, but there is a difference between a role-play opportunity and killing him off.
There are countless things the DM could do, completely legally, to screw over a player. The question is whether he should. Just because the player does something unexpected doesn't mean he should now be 'punished' by having his character gang-banged by a horde of paladins and their planetar mommys and solar daddies, or having his shadows turn against him when there are no rules to support it.
There is even a chance that it'll go completely unnoticed, especially if the player plans well. Make up a table and roll dice. In non-metagame terms, there is no reason doing this should draw any more ire than any other evil act that a group of evil PCs should perform. i.e. A lot, but not enough to TPK.
Modifying the Create Shadows ability would be a houserule. The player would need to know beforehand and, preferably, before the campaign starts.
No xp: why were the shadows there? That's right: he created them. Then he used them to his advantage in combat. How is this any different to, say, a battlefield control spell? An encounter's xp output isn't determined by how easily the players overcame it. It is determined by how difficult it is to overcome, given an arbitrary party of the same CR. If there are pre-existing factors that would help the players, you cut the xp - even if they don't use those factors at all. But if the players bring their own, then they should get full xp.