Ixhel, Scion of Atraxa

Flying, vigilance, toxic 2
Corrupted — At the beginning of your end step, each opponent who has three or more poison counters exiles the top card of their library face down. You may look at and play those cards for as long as they remain exiled, and you may spend mana as though it were mana of any color to cast those spells.

Forest

Atraxa, Praetors' Voice

Flying, vigilance, deathtouch, lifelink
At the beginning of your end step, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Virulent Wound

Put a -1/-1 counter on target creature. When that creature dies this turn, its controller gets a poison counter.

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.)

Orzhov Signet

Tezzeret's Gambit

({U/P} can be paid with either {U} or 2 life.)
Draw two cards, then proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Merciless Eviction

Choose one —
• Exile all artifacts.
• Exile all creatures.
• Exile all enchantments.
• Exile all planeswalkers.

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.)

Contagion Clasp

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

Grateful Apparition

Flying
Whenever this creature deals combat damage to a player or planeswalker, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Serum Snare

Return target nonland permanent to its owner's hand. If that permanent had mana value 3 or less, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Armored Scrapgorger

This creature gets +3/+0 as long as it has three or more oil counters on it.
{T}: Add one mana of any color.
Whenever this creature becomes tapped, exile target card from a graveyard and put an oil counter on this creature.

Opulent Palace

This land enters tapped.
{T}: Add {B}, {G}, or {U}.

Vishgraz, the Doomhive

Menace, toxic 1 (Players dealt combat damage by this creature also get a poison counter.)
When Vishgraz enters, create three 1/1 colorless Phyrexian Mite artifact creature tokens with toxic 1 and "This token can't block."
Vishgraz gets +1/+1 for each poison counter your opponents have.

Prologue to Phyresis

Each opponent gets a poison counter.
Draw a card.

Time Wipe

Return a creature you control to its owner's hand, then destroy all creatures.

Selesnya Signet

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.)

Corpsejack Menace

If one or more +1/+1 counters would be put on a creature you control, twice that many +1/+1 counters are put on it instead.

Putrefy

Destroy target artifact or creature. It can't be regenerated.

Blightbelly Rat

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

Aqueous Form

Enchant creature
Enchanted creature can't be blocked.
Whenever enchanted creature attacks, scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Unnatural Restoration

Return target permanent card from your graveyard to your hand. Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Swamp

Geth's Summons

Return up to one target creature card from your graveyard to the battlefield.
Corrupted — For each opponent who has three or more poison counters as you cast this spell, put up to one target creature card from that player's graveyard onto the battlefield under your control.

Exotic Orchard

{T}: Add one mana of any color that a land an opponent controls could produce.

Thirsting Roots

Choose one —
• Search your library for a basic land card, reveal it, put it into your hand, then shuffle.
• 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.)

Glistener Elf

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

Island

Venomous Brutalizer

Toxic 3 (Players dealt combat damage by this creature also get three poison counters.)
When this creature enters, you may pay {1}{G}. If you do, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Evolving Wilds

{T}, Sacrifice this land: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Tainted Observer

Flying
Toxic 1 (Players dealt combat damage by this creature also get a poison counter.)
Whenever another creature you control enters, you may pay {2}. If you do, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Bilious Skulldweller

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

Flux Channeler

Whenever you cast a noncreature spell, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

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.)

Jawbone Duelist

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

Atraxa's Skitterfang

This creature enters with three oil counters on it.
At the beginning of combat on your turn, you may remove an oil counter from this creature. When you do, target creature you control gains your choice of flying, vigilance, deathtouch, or lifelink until end of turn.

Vat Emergence

Put target creature card from a graveyard onto the battlefield under your control. Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Tyrranax Atrocity

Haste
Toxic 3 (Players dealt combat damage by this creature also get three poison counters.)

Necrogen Rotpriest

Toxic 2 (Players dealt combat damage by this creature also get two poison counters.)
Whenever a creature you control with toxic deals combat damage to a player, that player gets an additional poison counter.
{1}{B}{G}: Target creature you control with toxic gains deathtouch until end of turn.

Arcane Sanctum

This land enters tapped.
{T}: Add {W}, {U}, or {B}.

Forgotten Ancient

Whenever a player casts a spell, you may put a +1/+1 counter on this creature.
At the beginning of your upkeep, you may move any number of +1/+1 counters from this creature onto other creatures.

Mortify

Ezuri, Stalker of Spheres

When Ezuri enters, you may pay {3}. If you do, proliferate twice.
Whenever you proliferate, draw a card.

Corrupted Resolve

Counter target spell if its controller is poisoned.

Vraska's Fall

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

Copper Longlegs

Reach
{1}{G}, Sacrifice this creature: Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

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.)

Sandsteppe Citadel

This land enters tapped.
{T}: Add {W}, {B}, or {G}.

Scheming Aspirant

Whenever you proliferate, each opponent loses 2 life and you gain 2 life.

Deepglow Skate

When this creature enters, double the number of each kind of counter on any number of target permanents.

Core Prowler

Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)
When this creature dies, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Blight Mamba

Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)
{1}{G}: Regenerate this creature.

Contentious Plan

Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)
Draw a card.

Duneblast

Choose up to one creature. Destroy the rest.

Decimator Web

{4}, {T}: Target opponent loses 2 life, gets a poison counter, then mills six cards.

Dimir Signet

Crawling Chorus

Toxic 1 (Players dealt combat damage by this creature also get a poison counter.)
When this creature dies, create a 1/1 colorless Phyrexian Mite artifact creature token with toxic 1 and "This token can't block."

Seaside Citadel

This land enters tapped.
{T}: Add {G}, {W}, or {U}.

Pestilent Syphoner

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

Brokers Confluence

Choose three. You may choose the same mode more than once.
• Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)
• Target creature phases out. (Treat it and anything attached to it as though they don't exist until its controller's next turn.)
• Counter target activated or triggered ability.

Infectious Inquiry

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

Sublime Exhalation

Undaunted (This spell costs {1} less to cast for each opponent.)
Destroy all creatures.

Courage in Crisis

Put a +1/+1 counter on target creature, then proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Slaughter Singer

Toxic 2 (Players dealt combat damage by this creature also get two poison counters.)
Whenever another creature you control with toxic attacks, it gets +1/+1 until end of turn.

Arcane Signet

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

Glissa's Retriever

Haste, toxic 3 (Players dealt combat damage by this creature also get three poison counters.)
This creature can't be blocked by creatures with power 2 or less.
Corrupted — When this creature dies, exile it. When you do, return up to X target cards from your graveyard to your hand, where X is the number of opponents who have three or more poison counters.

Simic Signet

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.)

Fellwar Stone

Despark

Exile target permanent with mana value 4 or greater.

Planewide Celebration

Choose four. You may choose the same mode more than once.
• Create a 2/2 Citizen creature token that's all colors.
• Return target permanent card from your graveyard to your hand.
• Proliferate.
• You gain 4 life.

Plains

Thrummingbird

Flying
Whenever this creature deals combat damage to a player, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Unbounded Potential

Choose one —
• Put a +1/+1 counter on each of up to two target creatures.
• Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)
Entwine {3}{W} (Choose both if you pay the entwine cost.)

Grim Affliction

Put a -1/-1 counter on target creature, then proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Azorius Signet

Voidwing Hybrid

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

Command Tower

Mesmerizing Dose

Enchant creature
When this Aura enters, tap enchanted creature, then proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)
Enchanted creature doesn't untap during its controller's untap step.

Golgari Signet

Reaper of Sheoldred

Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)
Whenever a source deals damage to this creature, that source's controller gets a poison counter.