Namira, Lady of Rot

Whenever a creature card is put into an
opponent's graveyard from anywhere, put
a +1/+1 counter on Namira. At the
beginning of your upkeep, you may pay X
life, where X is the number of +1/+1
counters on Namira. If you do, return a
creature card from an opponent's
graveyard to the battlefield under your
control.