Bloated Contaminator

Trample
Toxic 1 (Players dealt combat damage by this creature also get a poison counter.)
Whenever Bloated Contaminator 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.)

Farseek

Search your library for a Plains, Island, Swamp, or Mountain card, put it onto the battlefield tapped, then shuffle.

Grateful Apparition

Flying
Whenever Grateful Apparition 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.)

Norn's Choirmaster

Flying, first strike
Whenever a commander you control enters or attacks, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Contagion Engine

When Contagion Engine 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.)

Cankerbloom

{1}, Sacrifice Cankerbloom: 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.)

Staff of Compleation

{T}, Pay 1 life: Destroy target permanent you own.
{T}, Pay 2 life: Add one mana of any color.
{T}, Pay 3 life: Proliferate.
{T}, Pay 4 life: Draw a card.
{5}: Untap Staff of Compleation.

Expand the Sphere

Look at the top six cards of your library. Put up to two land cards from among them onto the battlefield tapped and the rest on the bottom of your library in a random order. If you put fewer than two lands onto the battlefield this way, proliferate a number of times equal to the difference. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Evolution Sage

Landfall — Whenever a land you control enters, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Contaminant Grafter

Trample, toxic 1
Whenever one or more creatures you control deal combat damage to one or more players, proliferate.
Corrupted — At the beginning of your end step, if an opponent has three or more poison counters, draw a card, then you may put a land card from your hand onto the battlefield.

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.

Contagion Clasp

When Contagion Clasp 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.)

Doubling Season

If an effect would create one or more tokens under your control, it creates twice that many of those tokens instead.
If an effect would put one or more counters on a permanent you control, it puts twice that many of those counters on that permanent instead.

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.

Karn's Bastion

{T}: Add {C}.
{4}, {T}: Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Apostle's Blessing

({W/P} can be paid with either {W} or 2 life.)
Target artifact or creature you control gains protection from artifacts or from the color of your choice until end of turn.

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 Blight Mamba.

Lost Leonin

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

Cultivate

Search your library for up to two basic land cards, reveal those cards, put one onto the battlefield tapped and the other into your hand, then shuffle.

Spirit Mantle

Enchant creature
Enchanted creature gets +1/+1 and has protection from creatures.

Kodama's Reach

Glistening Sphere

Glistening Sphere enters tapped.
When Glistening Sphere enters, proliferate.
{T}: Add one mana of any color.
Corrupted — {T}: Add three mana of any one color. Activate only if an opponent has three or more poison counters.

Ajani, Sleeper Agent

Compleated ({G/W/P} can be paid with {G}, {W}, or 2 life. If life was paid, this planeswalker enters with two fewer loyalty counters.)
+1: Reveal the top card of your library. If it's a creature or planeswalker card, put it into your hand. Otherwise, you may put it on the bottom of your library.
−3: Distribute three +1/+1 counters among up to three target creatures. They gain vigilance until end of turn.
−6: You get an emblem with "Whenever you cast a creature or planeswalker spell, target opponent gets two poison counters."

Path to Exile

Exile target creature. Its controller may search their library for a basic land card, put that card onto the battlefield tapped, then shuffle.

Rampant Growth

Search your library for a basic land card, put that card onto the battlefield tapped, then shuffle.