Quest for the Gravelord

Whenever a creature dies, you may put a quest counter on Quest for the Gravelord.
Remove three quest counters from Quest for the Gravelord and sacrifice it: Create a 5/5 black Zombie Giant creature token.

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.)

Chill of the Grave

This spell costs {1} less to cast if you control a Zombie.
Tap target creature. It doesn't untap during its controller's next untap step.
Draw a card.

Island

Swamp

Rooftop Storm

You may pay {0} rather than pay the mana cost for Zombie creature spells you cast.

Champion of the Perished

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

Doomed Dissenter

When Doomed Dissenter dies, create a 2/2 black Zombie creature token.

Priest of Gix

When Priest of Gix enters, add {B}{B}{B}.

Compelling Deterrence

Return target nonland permanent to its owner's hand. Then that player discards a card if you control a Zombie.

Crawl from the Cellar

Return target creature card from your graveyard to your hand. Put a +1/+1 counter on up to one target Zombie you control.
Flashback {3}{B} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Dimir Aqueduct

Dimir Aqueduct enters tapped.
When Dimir Aqueduct enters, return a land you control to its owner's hand.
{T}: Add {U}{B}.

Hordewing Skaab

Flying
Other Zombies you control have flying.
Whenever one or more Zombies you control deal combat damage to one or more of your opponents, you may draw cards equal to the number of opponents dealt damage this way. If you do, discard that many cards.

Cleaver Skaab

{3}, {T}, Sacrifice another Zombie: Create two tokens that are copies of the sacrificed creature.

Vengeful Dead

Whenever Vengeful Dead or another Zombie dies, each opponent loses 1 life.

Empty the Laboratory

Sacrifice X Zombies, then reveal cards from the top of your library until you reveal a number of Zombie creature cards equal to the number of Zombies sacrificed this way. Put those cards onto the battlefield and the rest on the bottom of your library in a random order.

Lord of the Accursed

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

Dark Salvation

Target player creates X 2/2 black Zombie creature tokens, then up to one target creature gets -1/-1 until end of turn for each Zombie that player controls.