Twitch, the Plague Rat

Wither (This deals damage to creatures in the
form of -1/-1 counters.)
When Twitch, the Plague Rat enters the
battlefield put one -1/-1 counters on all creatures
you don't control.
Expunge — {1}{b}{b}: All creatures you don't
control with -1/-1 counters get -1/-1, then
remove all -1/-1 counters from those creatures.