Zareth, The Withering storm

Wither, trample
When Zareth, The withering storm attacks, Put a
-1/-1 counter on an opponent's creature
When a creature with -1/-1 counters dies, put that
many wither counters on that creatures controller
When Zareth does Combat damage, Do X
damage to any target where X is the number
of -1/-1 counters your opponents controls
and/or wither counters