Byorul, Anguish Warden

At the beginning of your pre-combat main
phase, you may put X nonland cards from your
graveyard on the bottom of your library. If you
do, you lose X life and the next creature spell
you cast this turn costs {x} less to cast.
The first time each turn that a card is put into
an opponent's graveyard from anywhere, you
gain 2 life.