Dymm Clan Cutthroat

Whenever Dymm Clan Cutthroat deals combat
damage to a creature, if it doesn't already have a
-1/-1 counter on it, prevent that damage and put
a -1/-1 counter on that creature.
{g}{2}: Double the amount of -1/-1 counters on
target creature that was dealt damage this turn.
Swiftly he slithers to deliver due punishment.