Soulless One

Soulless One's power and toughness are each equal to the number of Zombies on the battlefield plus the number of Zombie cards in all graveyards.

Zombie Cannibal

Whenever Zombie Cannibal deals combat damage to a player, you may exile target card from that player's graveyard.

Undead Warchief

Zombie spells you cast cost {1} less to cast.
Zombie creatures you control get +2/+1.

Endless Ranks of the Dead

At the beginning of your upkeep, create X 2/2 black Zombie creature tokens, where X is half the number of Zombies you control, rounded down.

Unholy Grotto

{T}: Add {C}.
{B}, {T}: Put target Zombie card from your graveyard on top of your library.

Swamp

Barrow Ghoul

At the beginning of your upkeep, sacrifice Barrow Ghoul unless you exile the top creature card of your graveyard.

Zombie Master

Other Zombie creatures have swampwalk. (They can't be blocked as long as defending player controls a Swamp.)
Other Zombies have "{B}: Regenerate this permanent."

Corpse Harvester

{1}{B}, {T}, Sacrifice a creature: Search your library for a Zombie card and a Swamp card, reveal them, put them into your hand, then shuffle.

Lord of the Undead

Other Zombie creatures get +1/+1.
{1}{B}, {T}: Return target Zombie card from your graveyard to your hand.

Champion of the Perished

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

Army of the Damned

Create thirteen tapped 2/2 black Zombie creature tokens.
Flashback {7}{B}{B}{B} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Gravecrawler

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

Gempalm Polluter

Cycling {B}{B} ({B}{B}, Discard this card: Draw a card.)
When you cycle Gempalm Polluter, you may have target player lose life equal to the number of Zombies on the battlefield.