Mountain

Koth, Fire of Resistance

+2: Search your library for a basic Mountain card, reveal it, put it into your hand, then shuffle.
−3: Koth, Fire of Resistance deals damage to target creature equal to the number of Mountains you control.
−7: You get an emblem with "Whenever a Mountain you control enters, this emblem deals 4 damage to any target."

Fire Diamond

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

Lightning Bolt

Lightning Bolt deals 3 damage to any target.

Solphim, Mayhem Dominus

If a source you control would deal noncombat damage to an opponent or a permanent an opponent controls, it deals double that damage to that player or permanent instead.
{1}{R/P}{R/P}, Discard two cards: Put an indestructible counter on Solphim, Mayhem Dominus. ({R/P} can be paid with either {R} or 2 life.)

Arcane Signet

{T}: Add one mana of any color in your commander's color identity.

Razorkin Needlehead

Razorkin Needlehead has first strike during your turn.
Whenever an opponent draws a card, Razorkin Needlehead deals 1 damage to them.

Abrade

Choose one —
• Abrade deals 3 damage to target creature.
• Destroy target artifact.

Lightning Strike

Lightning Strike deals 3 damage to any target.

Faithless Looting

Draw two cards, then discard two cards.
Flashback {2}{R} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Forgotten Cave

Forgotten Cave enters tapped.
{T}: Add {R}.
Cycling {R} ({R}, Discard this card: Draw a card.)

Unexpected Windfall

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 artifact: Add one mana of any color.")

Valakut, the Molten Pinnacle

Valakut, the Molten Pinnacle enters tapped.
Whenever a Mountain you control enters, if you control at least five other Mountains, you may have Valakut, the Molten Pinnacle deal 3 damage to any target.
{T}: Add {R}.

Shock

Chain Reaction

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

Tibalt's Trickery

Counter target spell. Choose 1, 2, or 3 at random. Its controller mills that many cards, then exiles cards from the top of their library until they exile a nonland card with a different name than that spell. They may cast that card without paying its mana cost. Then they put the exiled cards on the bottom of their library in a random order.

Fellwar Stone

{T}: Add one mana of any color that a land an opponent controls could produce.

Erebor Flamesmith

Whenever you cast an instant or sorcery spell, Erebor Flamesmith deals 1 damage to each opponent.

Gimli, Counter of Kills

Trample
Whenever a creature an opponent controls dies, Gimli, Counter of Kills deals 1 damage to that creature's controller.

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.

Cathartic Pyre

Choose one —
• Cathartic Pyre deals 3 damage to target creature or planeswalker.
• Discard up to two cards, then draw that many cards.

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.

Commander's Sphere

{T}: Add one mana of any color in your commander's color identity.
Sacrifice Commander's Sphere: Draw a card.

Fiery Inscription

When Fiery Inscription enters, the Ring tempts you.
Whenever you cast an instant or sorcery spell, Fiery Inscription deals 2 damage to each opponent.

Blasphemous Act

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

Impact Tremors

Whenever a creature you control enters, this enchantment deals 1 damage to each opponent.

Swiftfoot Boots

Equipped creature has hexproof and haste. (It can't be the target of spells or abilities your opponents control. It can attack and {T} no matter when it came under your control.)
Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)

Diamond Pick-Axe

Indestructible (Effects that say "destroy" don't destroy this artifact.)
Equipped creature gets +1/+1 and has "Whenever this creature attacks, create a Treasure token." (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")
Equip {2}

Thrill of Possibility

As an additional cost to cast this spell, discard a card.
Draw two cards.

Electrickery

Electrickery deals 1 damage to target creature you don't control.
Overload {1}{R} (You may cast this spell for its overload cost. If you do, change "target" in its text to "each.")

Sol Ring

Arena of Glory

Arena of Glory enters tapped unless you control a Mountain.
{T}: Add {R}.
{R}, {T}, Exert Arena of Glory: Add {R}{R}. If that mana is spent on a creature spell, it gains haste until end of turn. (An exerted permanent won't untap during your next untap step.)

Mechanized Warfare

If a red or artifact source you control would deal damage to an opponent or a permanent an opponent controls, it deals that much damage plus 1 instead.

Genesis Chamber

Whenever a nontoken creature enters, if Genesis Chamber is untapped, that creature's controller creates a 1/1 colorless Myr artifact creature token.

Lightning Greaves

Equipped creature has haste and shroud. (It can't be the target of spells or abilities.)
Equip {0}

Big Score

Blood Moon

Gratuitous Violence

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

Chaos Warp

The owner of target permanent shuffles it into their library, then reveals the top card of their library. If it's a permanent card, they put it onto the battlefield.

Fiery Emancipation

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