Lightning Bolt

Lightning Bolt deals 3 damage to any target.

Viashino Pyromancer

When this creature enters, it deals 2 damage to target player or planeswalker.

Arc Lightning

Arc Lightning deals 3 damage divided as you choose among one, two, or three targets.

Ember Hauler

{1}, Sacrifice Ember Hauler: It deals 2 damage to any target.

Sarkhan, the Dragonspeaker

+1: Until end of turn, Sarkhan, the Dragonspeaker becomes a legendary 4/4 red Dragon creature with flying, indestructible, and haste. (He doesn't lose loyalty while he's not a planeswalker.)
−3: Sarkhan, the Dragonspeaker deals 4 damage to target creature.
−6: You get an emblem with "At the beginning of your draw step, draw two additional cards" and "At the beginning of your end step, discard your hand."

Foundry Street Denizen

Whenever another red creature you control enters, Foundry Street Denizen gets +1/+0 until end of turn.

Goblin Wardriver

Battle cry (Whenever this creature attacks, each other attacking creature gets +1/+0 until end of turn.)

Flametongue Kavu

When Flametongue Kavu enters, it deals 4 damage to target creature.

Bonesplitter

Mountain

Stormbreath Dragon

Flying, haste, protection from white
{5}{R}{R}: Monstrosity 3. (If this creature isn't monstrous, put three +1/+1 counters on it and it becomes monstrous.)
When Stormbreath Dragon becomes monstrous, it deals damage to each opponent equal to the number of cards in that player's hand.