Burning Curiosity

As an additional cost to cast this spell, you may blight 1. (You may put a -1/-1 counter on a creature you control.)
Exile the top two cards of your library. If this spell's additional cost was paid, exile the top three cards instead. Until the end of your next turn, you may play those cards.

Forest

Warren Torchmaster

At the beginning of combat on your turn, you may blight 1. When you do, target creature gains haste until end of turn. (To blight 1, put a -1/-1 counter on a creature you control.)

Fists of the Demigod

Enchant creature
As long as enchanted creature is black, it gets +1/+1 and has wither. (It deals damage to creatures in the form of -1/-1 counters.)
As long as enchanted creature is red, it gets +1/+1 and has first strike.

Auntie Ool, Cursewretch

Ward—Blight 2. (To blight 2, a player puts two -1/-1 counters on a creature they control.)
Whenever one or more -1/-1 counters are put on a creature, draw a card if you control that creature. If you don't control it, its controller loses 1 life.

Bogslither's Embrace

As an additional cost to cast this spell, blight 1 or pay {3}. (To blight 1, put a -1/-1 counter on a creature you control.)
Exile target creature.

Barbed Bloodletter

Flash
When this Equipment enters, attach it to target creature you control. That creature gains wither until end of turn. (It deals damage to creatures in the form of -1/-1 counters.)
Equipped creature gets +1/+2.
Equip {2}

Shadow Urchin

Whenever this creature attacks, blight 1. (Put a -1/-1 counter on a creature you control.)
Whenever a creature you control with one or more counters on it dies, exile that many cards from the top of your library. Until your next end step, you may play those cards.

Gristle Glutton

{T}, Blight 1: Discard a card. If you do, draw a card. (To blight 1, put a -1/-1 counter on a creature you control.)

Persistent Constrictor

At the beginning of each opponent's upkeep, they lose 1 life and you put a -1/-1 counter on up to one target creature they control.
Persist (When this creature dies, if it had no -1/-1 counters on it, return it to the battlefield under its owner's control with a -1/-1 counter on it.)

Noxious Hatchling

This creature enters with four -1/-1 counters on it.
Wither (This deals damage to creatures in the form of -1/-1 counters.)
Whenever you cast a black spell, remove a -1/-1 counter from this creature.
Whenever you cast a green spell, remove a -1/-1 counter from this creature.

Dream Seizer

Flying
When this creature enters, you may blight 1. If you do, each opponent discards a card. (To blight 1, put a -1/-1 counter on a creature you control.)

Bile-Vial Boggart

When this creature dies, put a -1/-1 counter on up to one target creature.

Canker Abomination

As this creature enters, choose an opponent. This creature enters with a -1/-1 counter on it for each creature that player controls.

Torture

Enchant creature
{1}{B}: Put a -1/-1 counter on enchanted creature.

Heirloom Auntie

This creature enters with two -1/-1 counters on it.
Whenever another creature you control dies, surveil 1, then remove a -1/-1 counter from this creature. (To surveil 1, look at the top card of your library. You may put it into your graveyard.)

Sting-Slinger

{1}{R}, {T}, Blight 1: This creature deals 2 damage to each opponent. (To blight 1, put a -1/-1 counter on a creature you control.)

Cankerbloom

{1}, Sacrifice this creature: Choose one —
• Destroy target artifact.
• Destroy target enchantment.
• Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Cinder Strike

As an additional cost to cast this spell, you may blight 1. (You may put a -1/-1 counter on a creature you control.)
Cinder Strike deals 2 damage to target creature. It deals 4 damage to that creature instead if this spell's additional cost was paid.

Brambleback Brute

This creature enters with two -1/-1 counters on it.
{1}{R}, Remove a counter from this creature: Target creature can't block this turn. Activate only as a sorcery.

Blight Rot

Put four -1/-1 counters on target creature.

Nest of Scarabs

Whenever you put one or more -1/-1 counters on a creature, create that many 1/1 black Insect creature tokens.

Hapatra, Vizier of Poisons

Whenever Hapatra deals combat damage to a player, you may put a -1/-1 counter on target creature.
Whenever you put one or more -1/-1 counters on a creature, create a 1/1 green Snake creature token with deathtouch.

Mountain

Rendclaw Trow

Wither (This deals damage to creatures in the form of -1/-1 counters.)
Persist (When this creature dies, if it had no -1/-1 counters on it, return it to the battlefield under its owner's control with a -1/-1 counter on it.)

Skinrender

When this creature enters, put three -1/-1 counters on target creature.

Carnifex Demon

Flying
This creature enters with two -1/-1 counters on it.
{B}, Remove a -1/-1 counter from this creature: Put a -1/-1 counter on each other creature.

Darkness Descends

Retched Wretch

When this creature dies, if it had a -1/-1 counter on it, return it to the battlefield under its owner's control and it loses all abilities.

Flourishing Defenses

Whenever a -1/-1 counter is put on a creature, you may create a 1/1 green Elf Warrior creature token.

Obelisk Spider

Reach
Whenever this creature deals combat damage to a creature, put a -1/-1 counter on that creature.
Whenever you put one or more -1/-1 counters on a creature, each opponent loses 1 life and you gain 1 life.

Chaos Spewer

When this creature enters, you may pay {2}. If you don't, blight 2. (To blight 2, put two -1/-1 counters on a creature you control.)

Black Sun's Zenith

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