Angel of Death

Flying, phase 3: Sacrifice a creature (When this
creature becomes target of a spell or an ability an
opponent controls or if you pay its phase costs, exile it
with 3 phase counters on it. Remove a phase counter
at the beginning of each turn. When there are no
counters left, put it back onto the battlefield.)
When Angel of Death enters the battlefield from
exile, you may pay {x}.
When Angel of Death enters the battlefield,
return target creature with mana value X from your graveyard to th