Seat of the Synod

Sugar Rush

Target creature gets +3/+0 until end of turn.
Draw a card.

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.)

Cartouche of Knowledge

Enchant creature you control
When Cartouche of Knowledge enters, draw a card.
Enchanted creature gets +1/+1 and has flying.

Contentious Plan

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

Island

Unstable Mutation

Enchant creature
Enchanted creature gets +3/+3.
At the beginning of the upkeep of enchanted creature's controller, put a -1/-1 counter on that creature.

Shadow Rift

Target creature gains shadow until end of turn. (It can block or be blocked by only creatures with shadow.)
Draw a card.

Prologue to Phyresis

Each opponent gets a poison counter.
Draw a card.

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.)

Vault of Whispers

Cradle of Safety

Flash
Enchant creature you control
When Cradle of Safety enters, enchanted creature gains hexproof until end of turn. (It can't be the target of spells or abilities your opponents control.)
Enchanted creature gets +1/+1.

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.)

Coat with Venom

Target creature gets +1/+2 and gains deathtouch until end of turn. (Any amount of damage it deals to a creature is enough to destroy it.)

Mistvault Bridge

Mistvault Bridge enters tapped.
Indestructible
{T}: Add {U} or {B}.

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.)
Blighted Agent can't be blocked.

Wedding Invitation

When Wedding Invitation enters, draw a card.
{T}, Sacrifice Wedding Invitation: Target creature can't be blocked this turn. If it's a Vampire, it also gains lifelink until end of turn.

Swamp

Supernatural Stamina

Until end of turn, target creature gets +2/+0 and gains "When this creature dies, return it to the battlefield tapped under its owner's control."

Chained Throatseeker

Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)
Chained Throatseeker can't attack unless defending player is poisoned.

Hunger of the Nim

Target creature gets +1/+0 until end of turn for each artifact you control.

Vivisurgeon's Insight

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

Eel Umbra

Flash (You may cast this spell any time you could cast an instant.)
Enchant creature
Enchanted creature gets +1/+1.
Umbra armor (If enchanted creature would be destroyed, instead remove all damage from it and destroy this Aura.)