Kooper, Endless Devour

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