Liliana, Death Mage

+1: Return up to one target creature card from your graveyard to your hand.
−3: Destroy target creature. Its controller loses 2 life.
−7: Target opponent loses 2 life for each creature card in their graveyard.

Lord of the Accursed

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

Graf Harvest

Zombies you control have menace. (They can't be blocked except by two or more creatures.)
{3}{B}, Exile a creature card from your graveyard: Create a 2/2 black Zombie creature token.

Swamp

Drag to the Underworld

This spell costs {X} less to cast, where X is your devotion to black. (Each {B} in the mana costs of permanents you control counts toward your devotion to black.)
Destroy target creature.

Diregraf Colossus

Diregraf Colossus enters the battlefield 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.

Abnormal Endurance

Until end of turn, target creature gets +2/+0 and gains "When this creature dies, return it to the battlefield tapped under its owner's control."

Grave Betrayal

Whenever a creature you don't control dies, return it to the battlefield under your control with an additional +1/+1 counter on it at the beginning of the next end step. That creature is a black Zombie in addition to its other colors and types.

Cemetery Recruitment

Return target creature card from your graveyard to your hand. If it's a Zombie card, draw a card.

Wight

Wight enters the battlefield tapped.
Life Drain — Whenever a creature dealt damage by Wight this turn dies, create a tapped 2/2 black Zombie creature token and exile that card.

Abattoir Ghoul

First strike
Whenever a creature dealt damage by Abattoir Ghoul this turn dies, you gain life equal to that creature's toughness.

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.

Pontiff of Blight

Extort (Whenever you cast a spell, you may pay {W/B}. If you do, each opponent loses 1 life and you gain that much life.)
Other creatures you control have extort. (If a creature has multiple instances of extort, each triggers separately.)

Unbreathing Horde

Unbreathing Horde enters the battlefield with a +1/+1 counter on it for each other Zombie you control and each Zombie card in your graveyard.
If Unbreathing Horde would be dealt damage, prevent that damage and remove a +1/+1 counter from it.

Death Baron

Skeletons you control and other Zombies you control get +1/+1 and have deathtouch.

Liliana's Scorn

Destroy target creature. You may search your library and/or graveyard for a card named Liliana, Death Mage, reveal it, and put it into your hand. If you search your library this way, shuffle.

Champion of the Perished

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

Gray Merchant of Asphodel

When Gray Merchant of Asphodel enters the battlefield, each opponent loses X life, where X is your devotion to black. You gain life equal to the life lost this way. (Each {B} in the mana costs of permanents you control counts toward your devotion to black.)