Phyrexian Altar

Sacrifice a creature: Add one mana of any color.

Carrion Feeder

Carrion Feeder can't block.
Sacrifice a creature: Put a +1/+1 counter on Carrion Feeder.

Gravecrawler

Gravecrawler can't block.
You may cast Gravecrawler from your graveyard as long as you control a Zombie.

Varina, Lich Queen

Whenever you attack with one or more Zombies, draw that many cards, then discard that many cards. You gain that much life.
{2}, Exile two cards from your graveyard: Create a tapped 2/2 black Zombie creature token.

Corpse Knight

Whenever another creature you control enters, each opponent loses 1 life.