Crash Through

Creatures you control gain trample until end of turn. (Each of those creature can deal excess combat damage to the player or planeswalker it's attacking.)
Draw a card.

Mountain

Crush

Imodane, the Pyrohammer

Whenever an instant or sorcery spell you control that targets only a single creature deals damage to that creature, Imodane deals that much damage to each opponent.

Flowstone Infusion

Target creature gets +2/-2 until end of turn.

Pyretic Ritual

Avatar Roku, Firebender

Whenever a player attacks, add six {R}. Until end of combat, you don't lose this mana as steps end.
{R}{R}{R}: Target creature gets +3/+0 until end of turn.

Flame Slash

Flame Slash deals 4 damage to target creature.

Electrodominance

Electrodominance deals X damage to any target. You may cast a spell with mana value X or less from your hand without paying its mana cost.

Crimson Wisps

Target creature becomes red and gains haste until end of turn. (It can attack and {T} this turn.)
Draw a card.

Overblaze

Each time target permanent would deal damage to a permanent or player this turn, it deals double that damage to that permanent or player instead.
Splice onto Arcane {2}{R}{R} (As you cast an Arcane spell, you may reveal this card from your hand and pay its splice cost. If you do, add this card's effects to that spell.)

Leyline Tyrant

Flying
You don't lose unspent red mana as steps and phases end.
When this creature dies, you may pay any amount of {R}. When you do, it deals that much damage to any target.

Battle Hymn

Torbran, Thane of Red Fell

If a red source you control would deal damage to an opponent or a permanent an opponent controls, it deals that much damage plus 2 instead.

Big Score

As an additional cost to cast this spell, discard a card.
Draw two cards and create two Treasure tokens. (They're artifacts with "{T}, Sacrifice this token: Add one mana of any color.")

Thermo-Alchemist

Defender
{T}: This creature deals 1 damage to each opponent.
Whenever you cast an instant or sorcery spell, untap this creature.

Lava Spike

Lava Spike deals 3 damage to target player or planeswalker.

Doublecast

When you next cast an instant or sorcery spell this turn, copy that spell. You may choose new targets for the copy.

Ensnared by the Mara

Each opponent faces a villainous choice — They exile cards from the top of their library until they exile a nonland card, then you may cast that card without paying its mana cost, or that player exiles the top four cards of their library and Ensnared by the Mara deals damage equal to the total mana value of those exiled cards to that player.

Ashling, Flame Dancer

You don't lose unspent red mana as steps and phases end.
Magecraft — Whenever you cast or copy an instant or sorcery spell, discard a card, then draw a card. If this is the second time this ability has resolved this turn, Ashling deals 2 damage to each opponent and each creature they control. If it's the third time, add {R}{R}{R}{R}.

Increasing Vengeance

Copy target instant or sorcery spell you control. If this spell was cast from a graveyard, copy that spell twice instead. You may choose new targets for the copies.
Flashback {3}{R}{R} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Mana Flare

Whenever a player taps a land for mana, that player adds one mana of any type that land produced.

Electro, Assaulting Battery

Flying
You don't lose unspent red mana as steps and phases end.
Whenever you cast an instant or sorcery spell, add {R}.
When Electro leaves the battlefield, you may pay {X}. When you do, he deals X damage to target player.

Ricochet Trap

If an opponent cast a blue spell this turn, you may pay {R} rather than pay this spell's mana cost.
Change the target of target spell with a single target.

Hit the Mother Lode

Discover 10. If the discovered card's mana value is less than 10, create a number of tapped Treasure tokens equal to the difference. (To discover 10, exile cards from the top of your library until you exile a nonland card with mana value 10 or less. Cast it without paying its mana cost or put it into your hand. Put the rest on the bottom in a random order.)

Desperate Ritual

Add {R}{R}{R}.
Splice onto Arcane {1}{R} (As you cast an Arcane spell, you may reveal this card from your hand and pay its splice cost. If you do, add this card's effects to that spell.)

Creative Technique

Demonstrate (When you cast this spell, you may copy it. If you do, choose an opponent to also copy it.)
Shuffle your library, then reveal cards from the top of it until you reveal a nonland card. Exile that card and put the rest on the bottom of your library in a random order. You may cast the exiled card without paying its mana cost.

Combust

This spell can't be countered.
Combust deals 5 damage to target white or blue creature. The damage can't be prevented.