Aether Sting

Whenever an opponent casts a creature spell, Aether Sting deals 1 damage to that player.

Spellshock

Whenever a player casts a spell, Spellshock deals 2 damage to that player.

Unleash Fury

Double the power of target creature until end of turn.

Volcanic Spray

Volcanic Spray deals 1 damage to each creature without flying and each player.
Flashback {1}{R} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Firebrand Archer

Whenever you cast a noncreature spell, this creature deals 1 damage to each opponent.

Rampaging Ferocidon

Menace
Players can't gain life.
Whenever another creature enters, Rampaging Ferocidon deals 1 damage to that creature's controller.

Repercussion

Whenever a creature is dealt damage, Repercussion deals that much damage to that creature's controller.

Burning Earth

Whenever a player taps a nonbasic land for mana, Burning Earth deals 1 damage to that player.