Garurumon, Waste Prowler

Whenever a permanent an opponent controls is
put into a graveyard from the battlefield, put a
+1/+1 counter on Garurumon, Waste Prowler.
At the beginning of your upkeep, if Garurumon
has one or more +1/+1 counters on it, you may
remove all of them. If you do, exile
each other nonland permanent with mana value
less than or equal to the number of counters
removed this way.