Maha, Its Feathers Night

Flying, trample
Ward—Discard a card.
Creatures your opponents control have base toughness 1.

Archfiend of Ifnir

Flying
Whenever you cycle or discard another card, put a -1/-1 counter on each creature your opponents control.
Cycling {2} ({2}, Discard this card: Draw a card.)

Mind Stone

{T}: Add {C}.
{1}, {T}, Sacrifice this artifact: Draw a card.

Arcane Signet

{T}: Add one mana of any color in your commander's color identity.

Desert of the Glorified

This land enters tapped.
{T}: Add {B}.
Cycling {1}{B} ({1}{B}, Discard this card: Draw a card.)

Sol Ring

Contagion Engine

When this artifact enters, put a -1/-1 counter on each creature target player controls.
{4}, {T}: Proliferate twice. (Choose any number of permanents and/or players, then give each another counter of each kind already there. Then do it again.)

Soul Snuffers

When this creature enters, put a -1/-1 counter on each creature.

Polluted Mire

This land enters tapped.
{T}: Add {B}.
Cycling {2} ({2}, Discard this card: Draw a card.)

Plague Spitter

At the beginning of your upkeep, this creature deals 1 damage to each creature and each player.
When this creature dies, it deals 1 damage to each creature and each player.

Swamp

Noxious Field

Enchant land
Enchanted land has "{T}: This land deals 1 damage to each creature and each player."

Black Sun's Zenith

Put X -1/-1 counters on each creature. Shuffle Black Sun's Zenith into its owner's library.

Midnight Banshee

Wither (This deals damage to creatures in the form of -1/-1 counters.)
At the beginning of your upkeep, put a -1/-1 counter on each nonblack creature.

Spitting Dilophosaurus

Whenever this creature enters or attacks, put a -1/-1 counter on up to one target creature.
Creatures your opponents control with -1/-1 counters on them can't block.

Necroskitter

Wither (This deals damage to creatures in the form of -1/-1 counters.)
Whenever a creature an opponent controls with a -1/-1 counter on it dies, you may return that card to the battlefield under your control.

Thran Dynamo

Piranha Marsh

This land enters tapped.
When this land enters, target player loses 1 life.
{T}: Add {B}.

Ghastly Demise

Destroy target nonblack creature if its toughness is less than or equal to the number of cards in your graveyard.

Blowfly Infestation

Whenever a creature dies, if it had a -1/-1 counter on it, put a -1/-1 counter on target creature.