Carrion Feeder

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

Thran Vigil

Whenever one or more artifact and/or creature cards leave your graveyard during your turn, put a +1/+1 counter on target creature you control.

Champion of the Perished

Whenever another Zombie you control enters, put a +1/+1 counter on Champion of the Perished.

Putrid Goblin

Persist (When this creature dies, if it had no -1/-1 counters on it, return it to the battlefield under its owner's control with a -1/-1 counter on it.)

Stitcher's Supplier

When Stitcher's Supplier enters or dies, mill three cards. (Put the top three cards of your library into your graveyard.)

Relentless Dead

Menace (This creature can't be blocked except by two or more creatures.)
When Relentless Dead dies, you may pay {B}. If you do, return it to its owner's hand.
When Relentless Dead dies, you may pay {X}. If you do, return another target Zombie creature card with mana value X from your graveyard to the battlefield.

Gravecrawler

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

Undead Augur

Whenever Undead Augur or another Zombie you control dies, you draw a card and you lose 1 life.