Blighted Agent

Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)
This creature can't be blocked.

Inexorable Tide

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

Unsummon

Return target creature to its owner's hand.

Steady Progress

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

Viral Drake

Flying
Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)
{3}{U}: Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Scry 1. (Look at the top card of your library. You may put that card on the bottom.)
Draw a card.

Corrupted Resolve

Counter target spell if its controller is poisoned.

Prologue to Phyresis

Each opponent gets a poison counter.
Draw a card.

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.)

Fuel for the Cause

Counter target spell, then proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)