Contravos, Compleated Purifier

Wither

Whenever a creature an opponent controls with a -1/-1 counter dies, you gain 1 life, draw a card, and put a +1/+1 counter on Contravos.

{2}, {t}: Proliferate.

{b}{r}{g}, Remove three +1/+1 counters from Contravos, {t}: Contravos deals X damage to target player, where X is the number of -1/-1 counters on all permanents that player controls.