Arunkanem, Lord of Purgatory

Flying, Wither (This deals damage to creatures in
the form of -1/-1 counters.)
This creature must be blocked if able and doesn't
untap during your untap step unless you sacrifice
a creature. Whenever a creature an opponents
control leaves the battlefield due to -1/-1 counters, remove all -1/-1 counters from that creature and
it reenters the battlefield under your control at
the beginning of your next end step. When that creature dies on your side of the battlefield, exile
it instead.