Corpseborn Ascendant

Lifelink
At the beginning of your upkeep, if you control three or more Zombie Knights, put
a +1/+1 counter on Corpseborn Ascendant.
Whenever a creature card is put into an opponent's graveyard from anywhere, you
may pay {1}{w}{b}. If you do, you gain life
equal to that creature's toughness.