Diregraf Colossus

This creature enters with a +1/+1 counter on it for each Zombie card in your graveyard.
Whenever you cast a Zombie spell, create a tapped 2/2 black Zombie creature token.

Elas il-Kor, Sadistic Pilgrim

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

Headless Rider

Whenever this creature or another nontoken Zombie you control dies, create a 2/2 black Zombie creature token.

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."

Plains

Shepherd of Rot

{T}: Each player loses 1 life for each Zombie on the battlefield.

Champion of the Perished

Whenever another Zombie you control enters, put a +1/+1 counter on this creature.

Undead Warchief

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

Cemetery Reaper

Other Zombie creatures you control get +1/+1.
{2}{B}, {T}: Exile target creature card from a graveyard. Create a 2/2 black Zombie creature token.

Wayward Servant

Whenever another Zombie you control enters, each opponent loses 1 life and you gain 1 life.

Tomb Tyrant

Other Zombies you control get +1/+1.
{2}{B}, {T}, Sacrifice a creature: Return a Zombie creature card at random from your graveyard to the battlefield. Activate only during your turn and only if there are at least three Zombie creature cards in your graveyard.

Ratadrabik of Urborg

Vigilance, ward {2}
Other Zombies you control have vigilance.
Whenever another legendary creature you control dies, create a token that's a copy of that creature, except it's not legendary and it's a 2/2 black Zombie in addition to its other colors and types.

God-Eternal Oketra

Double strike
Whenever you cast a creature spell, create a 4/4 black Zombie Warrior creature token with vigilance.
When God-Eternal Oketra dies or is put into exile from the battlefield, you may put it into its owner's library third from the top.

Death Baron

Skeletons you control and other Zombies you control get +1/+1 and have deathtouch. (Any amount of damage they deal to a creature is enough to destroy it.)

Zul Ashur, Lich Lord

Ward—Pay 2 life. (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays 2 life.)
{T}: You may cast target Zombie creature card from your graveyard this turn.

Gravecrawler

This creature can't block.
You may cast this card from your graveyard as long as you control a Zombie.

Cruel Celebrant

Whenever this creature or another creature or planeswalker you control dies, each opponent loses 1 life and you gain 1 life.

Binding Mummy

Whenever another Zombie you control enters, you may tap target artifact or creature.

Teysa Karlov

If a creature dying causes a triggered ability of a permanent you control to trigger, that ability triggers an additional time.
Creature tokens you control have vigilance and lifelink.

Lord of the Undead

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

Swamp

Lord of the Accursed

Other Zombies you control get +1/+1.
{1}{B}, {T}: All Zombies gain menace until end of turn.

Athreos, God of Passage

Indestructible
As long as your devotion to white and black is less than seven, Athreos isn't a creature.
Whenever another creature you own dies, return it to your hand unless target opponent pays 3 life.

Ayara, First of Locthwain

Whenever Ayara or another black creature you control enters, each opponent loses 1 life and you gain 1 life.
{T}, Sacrifice another black creature: Draw a card.

On Wings of Gold

Creatures you control that are Zombies and/or tokens get +1/+1 and have flying.
Whenever one or more cards leave your graveyard, create a 1/1 white Zombie creature token.

Cryptbreaker

{1}{B}, {T}, Discard a card: Create a 2/2 black Zombie creature token.
Tap three untapped Zombies you control: You draw a card and you lose 1 life.

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.

Undead Augur

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

Sidisi, Undead Vizier

Deathtouch
Exploit (When this creature enters, you may sacrifice a creature.)
When Sidisi exploits a creature, you may search your library for a card, put it into your hand, then shuffle.