Chain Reaction

Chain Reaction deals X damage to each creature, where X is the number of creatures on the battlefield.

Furnace of Rath

If a source would deal damage to a permanent or player, it deals double that damage to that permanent or player instead.

Thran Dynamo

Rolling Earthquake

Rolling Earthquake deals X damage to each creature without horsemanship and each player.

Dictate of the Twin Gods

Flash
If a source would deal damage to a permanent or player, it deals double that damage to that permanent or player instead.

Mizzium Mortars

Mizzium Mortars deals 4 damage to target creature you don't control.
Overload {3}{R}{R}{R} (You may cast this spell for its overload cost. If you do, change "target" in its text to "each.")

Fire Diamond

Fire Diamond enters tapped.
{T}: Add {R}.

Toralf's Hammer

Equipped creature has "{1}{R}, {T}, Unattach Toralf's Hammer: It deals 3 damage to any target. Return Toralf's Hammer to its owner's hand."
Equipped creature gets +3/+0 as long as it's legendary.
Equip {1}{R}

Toralf, God of Fury

Trample
Whenever a creature or planeswalker an opponent controls is dealt excess noncombat damage, Toralf deals damage equal to the excess to any target other than that permanent.

Toralf, God of Fury // Toralf's Hammer

Blasphemous Act

This spell costs {1} less to cast for each creature on the battlefield.
Blasphemous Act deals 13 damage to each creature.

Earthquake

Earthquake deals X damage to each creature without flying and each player.

Starstorm

Starstorm deals X damage to each creature.
Cycling {3} ({3}, Discard this card: Draw a card.)

Mountain

Chandra's Incinerator

This spell costs {X} less to cast, where X is the total amount of noncombat damage dealt to your opponents this turn.
Trample
Whenever a source you control deals noncombat damage to an opponent, Chandra's Incinerator deals that much damage to target creature or planeswalker that player controls.