Grusha, Grown to Kill

When a creature you control leaves the
battlefield, you may pay {b/g}: place a +1/+1
counter on Grusha, Grown to Kill.
When a creature you control enters the
battlefield, you may pay {b/g} and remove
+1/+1 counters from Grusha, Grown to Kill:
Deal X damage to any target, where X is equal
to the amount of +1/+1 counters you removed
in this way.