Wall of Smoke

Defender, Reverb (Whenever this creature blocks a creature, it deals X damage to that creature at end of combat, where X is equal to this creature's toughness
minus that creature's power.)
At the beginning of your upkeep, pay {r} or
sacrifice Wall of Smoke.
{t}: Tap target creature Wall of Smoke has
blocked this turn. It doesn't untap as normal
during its controller's next untap step.