Instant, 1B (2) Change the target of target spell with a single target. You lose life equal to that spell's converted mana cost. "Do the innocent pay for the crimes of the guilty? Of course they do. That's the fate of the weak." —Nicol Bolas
Illus. Thomas M. Baxa
If there are no other legal targets, the target does not change but you still lose the life. [Planar Chaos FAQ 2006/12/13]
If a spell targets multiple things, you cannot use this spell on it even if all the other targets have become illegal. [Planar Chaos FAQ 2006/12/13]
If a spell targets the same thing multiple times, you cannot use this spell on it. [Planar Chaos FAQ 2006/12/13]
If you change a spell to target this spell, this spell will resolve first and leave that spell having an illegal target when it resolves. [Planar Chaos FAQ 2006/12/13]
A spell cannot target itself. See Rule G20.3f. [D'Angelo 2007/01/31]