Memento Mori

Memento Mori casts with 6 {e}.
Equipped creature has +3/+1 as long as this artifact has one {e}.
When equipped creature attacks or blocks,
remove a charge counter after damage is resolved.
Firefly - If enchanted creature kills a creature an opponent controls, add {e}until you have six
Equip {7} / Equip Guardian {3}