Enigma Drake

Flying
Enigma Drake's power is equal to the number of instant and sorcery cards in your graveyard.

Guttersnipe

Whenever you cast an instant or sorcery spell, this creature deals 2 damage to each opponent.

Giant Cindermaw

Trample (This creature can deal excess combat damage to the player or planeswalker it's attacking.)
Players can't gain life.

Balmor, Battlemage Captain

Flying
Whenever you cast an instant or sorcery spell, creatures you control get +1/+0 and gain trample until end of turn.

Brineborn Cutthroat

Flash (You may cast this spell any time you could cast an instant.)
Whenever you cast a spell during an opponent's turn, put a +1/+1 counter on this creature.

Firespitter Whelp

Flying
Whenever you cast a noncreature or Dragon spell, Firespitter Whelp deals 1 damage to each opponent.

Exclusion Mage

When this creature enters, return target creature an opponent controls to its owner's hand.