Valeria, the Eternal Seeker

Lifelink
Whenever a creature card is put into an
opponent's graveyard from anywhere, you may
pay {1}{w}{b}. If you do, return that card to the
battlefield under your control. It's a black and
white Zombie Knight in addition to its other
types.
At the beginning of your upkeep, if you control
three or more Zombie Knights, each opponent sacrifices a creature.