The Wither, Bane of Life

Flying, Wither, Hexproof
Whenever The Wither destroys another creature,
put three +1/+1 counters on The Wither.
Whenever another creature would deal damage
to The Wither, instead put that many -1/-1
counters on The Wither.
They said no one would be mad enough to build it,
and then they died.