Burglar Rat

When Burglar Rat enters the battlefield, each opponent discards a card.

Flensermite

Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)
Lifelink (Damage dealt by this creature also causes you to gain that much life.)

Coercion

Target opponent reveals their hand. You choose a card from it. That player discards that card.

Phyresis

Enchant creature
Enchanted creature has infect. (It deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)

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.)

Dune Mover

Toxic 1 (Players dealt combat damage by this creature also get a poison counter.)
When Dune Mover enters the battlefield, you may search your library for a basic land card, reveal it, then shuffle and put that card on top.

Mind Drain

Target opponent discards two cards, mills a card, and loses 1 life. You gain 1 life. (To mill a card, a player puts the top card of their library into their graveyard.)

Plague Stinger

Flying
Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)

Ashiok's Adept

Heroic — Whenever you cast a spell that targets Ashiok's Adept, each opponent discards a card.

Vicious Rumors

Vicious Rumors deals 1 damage to each opponent. Each opponent discards a card, then mills a card. You gain 1 life.

Contagious Nim

Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)

Tainted Strike

Target creature gets +1/+0 and gains infect until end of turn. (It deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)

Wrench Mind

Target player discards two cards unless they discard an artifact card.

Dark Inquiry

Target opponent reveals their hand. You choose a nonland card from it. That player discards that card.

Distress

Target player reveals their hand. You choose a nonland card from it. That player discards that card.

Divest

Target player reveals their hand. You choose an artifact or creature card from it. That player discards that card.

Sheoldred's Headcleaver

Menace
Toxic 2 (Players dealt combat damage by this creature also get two poison counters.)

Infectious Inquiry

You draw two cards and you lose 2 life. Each opponent gets a poison counter.

Virus Beetle

When Virus Beetle enters the battlefield, each opponent discards a card.

Vraska's Fall

Each opponent sacrifices a creature or planeswalker and gets a poison counter.

Elderfang Disciple

When Elderfang Disciple enters the battlefield, each opponent discards a card.

Pestilent Syphoner

Flying
Toxic 1 (Players dealt combat damage by this creature also get a poison counter.)

Blightbelly Rat

Toxic 1 (Players dealt combat damage by this creature also get a poison counter.)
When Blightbelly Rat dies, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Anoint with Affliction

Exile target creature if it has mana value 3 or less.
Corrupted — Exile that creature instead if its controller has three or more poison counters.

Swamp

Okiba-Gang Shinobi

Ninjutsu {3}{B} ({3}{B}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)
Whenever Okiba-Gang Shinobi deals combat damage to a player, that player discards two cards.

Relic Putrescence

Enchant artifact
Whenever enchanted artifact becomes tapped, its controller gets a poison counter.

Ravenous Rats

When Ravenous Rats enters the battlefield, target opponent discards a card.

Mind Rot

Cry of Contrition

Target player discards a card.
Haunt (When this spell card is put into a graveyard after resolving, exile it haunting target creature.)
When the creature Cry of Contrition haunts dies, target player discards a card.

Corrupt Court Official

When Corrupt Court Official enters the battlefield, target opponent discards a card.

Duress

Target opponent reveals their hand. You choose a noncreature, nonland card from it. That player discards that card.

Ichorclaw Myr

Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)
Whenever Ichorclaw Myr becomes blocked, it gets +2/+2 until end of turn.