Experimental Augury

Look at the top three cards of your library. Put one of them into your hand and the rest on the bottom of your library in any order. Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Drown in Ichor

Target creature gets -4/-4 until end of turn. Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Reject Imperfection

Counter target spell. If that spell's mana value was 3 or less, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Vraska's Fall

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

Island

Swamp

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.

Bilious Skulldweller

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

Bring the Ending

Counter target spell unless its controller pays {2}.
Corrupted — Counter that spell instead if its controller has three or more poison counters.

Underground River

{T}: Add {C}.
{T}: Add {U} or {B}. Underground River deals 1 damage to you.

Darkslick Shores

Darkslick Shores enters tapped unless you control two or fewer other lands.
{T}: Add {U} or {B}.

Shipwreck Marsh

Shipwreck Marsh enters tapped unless you control two or more other lands.
{T}: Add {U} or {B}.

Voidwing Hybrid

Flying
Toxic 1 (Players dealt combat damage by this creature also get a poison counter.)
When you proliferate, return Voidwing Hybrid from your graveyard to your hand.

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.)

Whisper of the Dross

Target creature gets -1/-1 until end of turn. Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Mirrex

{T}: Add {C}.
{T}: Add one mana of any color. Activate only if Mirrex entered this turn.
{3}, {T}: Create a 1/1 colorless Phyrexian Mite artifact creature token with toxic 1 and "This creature can't block." (Players dealt combat damage by it also get a poison counter.)

Prologue to Phyresis

Each opponent gets a poison counter.
Draw a card.

Distorted Curiosity

Corrupted — This spell costs {2} less to cast if an opponent has three or more poison counters.
Draw two cards.