Tennisball Demon Thing

Flying, Deathtouch
When Tennisball Demon Thing enters the battlefield, put a -1/-1 counter on all creatures your opponent controls.
At your end step, put an additional -1/-1 counter on any creature with a -1/-1 counter.
{5}{b}{b}{b}{b}{b} Double the number of -1/-1 counters on all creatures, exile Tennisball Demon Thing.