Maerlyn's Black Thirteen

Equip 2
When this artifact is equipped, and either the creature it is equipped to dies, or kills another creature, place a +1/+1 counter on Black Thirteen.
When thirteen +1/+1 counters have been placed on this artifact, exile Black Thirteen and put the planeswalker, Macestopholies, Pit Fiend of the Mortal Plane, in your hand.