Corrupted Wyrm

You may exert this card as it attacks (it gets +2/+2 and doesn't untap during your next untap step.)
Afflict 4 (If this creature becomes blocked, blocking opponent loses 4 life)
If this creature is exerted and becomes blocked destroy target non-blocking, non black creature.
Heroic- If this creature becomes the target of a spell or ability, untap it, it gains flying until end of turn.