Zero, Master Ambusher

Cooldown (Activated abilities of this creature cannot be
activated for as long as it has cooldown counters on it. At the
beginning of your upkeep, remove a cooldown counter from
this creature.)
{t}: Exile Zero, Master Ambusher face-down. Turn it
face-up at the beginning of the next end step then
put a cooldown counter on it. Activate this ability
during any main phase.
{w}{b}: Turn Zero, Master Ambusher face-up. Put
two cooldown counters on it then destroy
target attacking creature