Corwin, Plague Doctor

When this creature enters the battlefield or
another creature looses -1/-1 counters create a
1/1 black Bird creature token with Flying,
Lifelink, and Deathtouch.
{1}{w/b}{w/b} or {w/b}, Sacrifice another creature: Remove
or put 4 -1/-1 counters on target creature.
Whenever a creature dies you gain 1 life.