Sarulf, Realm Eater

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 mana
value less than or equal to the number of
counters removed this way.