Army Assasin

At the beginning of your upkeep put an agility
counter on this creature.
{w} : Remove an agility counter from this creature,
if you do this creature gets First Strike until end
of the turn.
{b} : Remove 2 agility counters from this creature,
if you do this creature gets Death Touch until
end of the turn.
Whenever this creature kills a creature, put an
agility counter on this creature.