Executioner of the Damned

Pact - Sacrifice another creature (When this
creature enters the battlefield or at the beginning of
your upkeep, you may sacrifice another creature to
form a pact with it until you form another pact.)
Flying
Whenever Executioner of the Damned attacks, if
you have a pact with it, destroy target creature an opponent controls. You lose life equal to that creature's toughness.