Venomous Amulet

As long as equipped creature has less than two
+1/+1 counters on it, it has double strike.
As long as equipped creature has exactly two
+1/+1 counters on it, it has double strike and deathtouch.
As long as equipped creature has three or more
+1/+1 counters on it, it has deathtouch.
Equip {3} ({3}: Attach to target creature you
control. Equip only as a sorcery.)