Hmm. I think I prefer the Final-Sting Faerie / Orzhov Euthanist approach; this one approaches having memory issues. (It is an effect occasionally seen on rares, such as Shriveling Rot, but I think the Fatal Blow approach is cleaner.)

I think the ability has value enough so that the memory issues can be handwaved away. It would be a rare situation where players forgot which creature got targeted, and if it happened on this turn. It probably does need to hop out of the common slot, though. We shouldn't regularly be having minor timing issues.

My big problem with the card is that it will either work, or it won't. Direct damage means nothing with this thing. You just point and click, and assuming your opponent doesn't have some damage prevention or a counterspell, there won't be any surprise. Combat damage is where this creature does what he does well, since he raises interesting questions for combat... so that being the case, why not just have him focus on combat? I prefer "When that creature is dealt combat damage" or "When that creature blocks". Less memory issues that way, too.

Dunno; this way round it can work as a nice "Ok, that creature there. Now; I attack. Fancy not blocking?"

The other way round it works as a "You blocked! Gotcha!"

Not sure which is blackier, really - black likes both impending doom and making you regret things.

Okay, I guess you've persuaded me that there can be some value to doing it this way round too.