Deepwood Stalkers

Skulk
Decay 2 (This creature enters the battlefield with 2 +1/+1 counters on it. Whenever this creature blocks or becomes blocked, remove a +1/+1 counter from it.)
Whenever Deepwood Stalkers deals combat damage to a player, put a +1/+1 counter on it.
The more you fear them, the more of them appear.