Mountain

Kiln Fiend

Whenever you cast an instant or sorcery spell, Kiln Fiend gets +3/+0 until end of turn.

Monastery Swiftspear

Haste
Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)

Reckless Impulse

Exile the top two cards of your library. Until the end of your next turn, you may play those cards.

Burning Prophet

Whenever you cast a noncreature spell, Burning Prophet gets +1/+0 until end of turn, then scry 1.

Downhill Charge

You may sacrifice a Mountain rather than pay this spell's mana cost.
Target creature gets +X/+0 until end of turn, where X is the number of Mountains you control.

Mine Collapse

If it's your turn, you may sacrifice a Mountain rather than pay this spell's mana cost.
Mine Collapse deals 5 damage to target creature or planeswalker.

Ghitu Lavarunner

As long as there are two or more instant and/or sorcery cards in your graveyard, Ghitu Lavarunner gets +1/+0 and has haste.

Shard Volley

As an additional cost to cast this spell, sacrifice a land.
Shard Volley deals 3 damage to any target.

Magma Jet

Magma Jet deals 2 damage to any target. Scry 2.

Chain Lightning

Chain Lightning deals 3 damage to any target. Then that player or that permanent's controller may pay {R}{R}. If the player does, they may copy this spell and may choose a new target for that copy.

Lightning Bolt

Lightning Bolt deals 3 damage to any target.

Lightning Axe

As an additional cost to cast this spell, discard a card or pay {5}.
Lightning Axe deals 5 damage to target creature.

Lightning Strike

Lightning Strike deals 3 damage to any target.

Festival Crasher

Whenever you cast an instant or sorcery spell, Festival Crasher gets +2/+0 until end of turn.

Scouring Sands

Scouring Sands deals 1 damage to each creature your opponents control. Scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Fireblast

You may sacrifice two Mountains rather than pay this spell's mana cost.
Fireblast deals 4 damage to any target.

Lava Dart

Lava Dart deals 1 damage to any target.
Flashback—Sacrifice a Mountain. (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Lava Spike

Lava Spike deals 3 damage to target player or planeswalker.

Kessig Flamebreather

Whenever you cast a noncreature spell, Kessig Flamebreather deals 1 damage to each opponent.

Experimental Synthesizer

When Experimental Synthesizer enters or leaves the battlefield, exile the top card of your library. Until end of turn, you may play that card.
{2}{R}, Sacrifice Experimental Synthesizer: Create a 2/2 white Samurai creature token with vigilance. Activate only as a sorcery.