Well, this is a tricky one, but here goes:
Cinder Snake
<cost>
Creature -- Snake
3/3
At the end of the turn Cinder Snake comes into play, sacrifice it unless it was dealt damage by a spell you control.
So the idea is, instead of
discarding a burn spell, you play it, then immediately have to
cast a burn spell on it or else it will die (this will make for some AWESOME flavor text btw). That means increasing the toughness so it will survive the spell, but that's okay because you'd BETTER get a nice creature for all the trouble you're going through.
I'm not seeing how this is black in any way, though.
Option #2:
Cinder Snake

Creature -- Snake
3/3
Defender
Whenever Cinder Snake is dealt damage by a source you control, it loses defender until end of turn.
That one is a little simpler, but not quite as strong. It sits there being all lazy until you poke it in the butt, at which point it gets up and goes lumbering off to smash the hell out of something.