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."

Thundering Rebuke

Thundering Rebuke deals 4 damage to target creature or planeswalker.

Molten Rebuke

Choose one or both —
• Molten Rebuke deals 5 damage to target creature or planeswalker.
• Destroy target Equipment.

The Red Terror

Advanced Species — Whenever a red source you control deals damage to one or more permanents and/or players, put a +1/+1 counter on The Red Terror.

Abrade

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

Sol Ring

Blazing Volley

Blazing Volley deals 1 damage to each creature your opponents control.

Obliterating Bolt

Obliterating Bolt deals 4 damage to target creature or planeswalker. If that creature or planeswalker would die this turn, exile it instead.

Guttersnipe

Whenever you cast an instant or sorcery spell, Guttersnipe deals 2 damage to each opponent.

Tectonic Hazard

Tectonic Hazard deals 1 damage to each opponent and each creature they control.

Hexgold Slash

Hexgold Slash deals 2 damage to target creature. If that creature has toxic, Hexgold Slash deals 4 damage to that creature instead.

Unleash Shell

Unleash Shell deals 5 damage to target creature or planeswalker and 2 damage to that permanent's controller.

Hazardous Blast

Hazardous Blast deals 1 damage to each creature your opponents control. Creatures your opponents control can't block this turn.

Mountain

Arcane Signet

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

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.)