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.)

Mesmerizing Dose

Enchant creature
When Mesmerizing Dose 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.

Tolarian Terror

This spell costs {1} less to cast for each instant and sorcery card in your graveyard.
Ward {2} (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {2}.)

Faerie Seer

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.)

Dismal Backwater

Dismal Backwater enters tapped.
When Dismal Backwater enters, you gain 1 life.
{T}: Add {U} or {B}.

Nightscape Familiar

Blue spells and red spells you cast cost {1} less to cast.
{1}{B}: Regenerate Nightscape Familiar.

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.)

Swamp

Spell Pierce

Counter target noncreature spell unless its controller pays {2}.

Vraska's Fall

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

Stormscape Familiar

Flying
White spells and black spells you cast cost {1} less to cast.

Counterspell

Prologue to Phyresis

Each opponent gets a poison counter.
Draw a card.

Infectious Inquiry

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

Island

Sign in Blood

Target player draws two cards and loses 2 life.

Pestilent Syphoner

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