Cú Chulainn's Battle Axe

Equip {3}
Whenever the equipped creature destroys a
creature in combat, put a soul counter on this artifact.
Equipped creature gets +2/+X, where X is the
total number of soul counters on this artifact.
{2}{g/w}, Destroy this artifact: Target creature gets
+X/-X, where X is the total number of soul
counters on this artifact.