Battlefield Forge

{T}: Add {C}.
{T}: Add {R} or {W}. Battlefield Forge deals 1 damage to you.

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."

End the Festivities

End the Festivities deals 1 damage to each opponent and each creature and planeswalker they control.

Falkenrath Perforator

Whenever Falkenrath Perforator attacks, it deals 1 damage to defending player.

Capricious Hellraiser

This spell costs {3} less to cast if you have nine or more cards in your graveyard.
Flying
When Capricious Hellraiser enters, exile three cards at random from your graveyard. Choose a noncreature, nonland card from among them and copy it. You may cast the copy without paying its mana cost.

Mountain

The Fall of Kroog

Choose target opponent. Destroy target land that player controls. The Fall of Kroog deals 3 damage to that player and 1 damage to each creature they control.

Lambholt Ravager

Whenever you cast a noncreature spell, Lambholt Ravager deals 2 damage to each opponent.
Nightbound (If a player casts at least two spells during their own turn, it becomes day next turn.)

Lambholt Raconteur

Whenever you cast a noncreature spell, Lambholt Raconteur deals 1 damage to each opponent.
Daybound (If a player casts no spells during their own turn, it becomes night next turn.)

Lambholt Raconteur // Lambholt Ravager

Call In a Professional

Players can't gain life this turn. Damage can't be prevented this turn. Call In a Professional deals 3 damage to any target. (Shield counters don't prevent this damage as they're removed.)

Unleash Shell

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

Dire-Strain Anarchist

Menace, haste
Whenever Dire-Strain Anarchist attacks, it deals 2 damage to each of up to one target creature, up to one target player, and/or up to one target planeswalker.
Nightbound (If a player casts at least two spells during their own turn, it becomes day next turn.)

Volatile Arsonist

Menace, haste
Whenever Volatile Arsonist attacks, it deals 1 damage to each of up to one target creature, up to one target player, and/or up to one target planeswalker.
Daybound (If a player casts no spells during their own turn, it becomes night next turn.)

Volatile Arsonist // Dire-Strain Anarchist

Kessig Flamebreather

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

Pyrrhic Blast

As an additional cost to cast this spell, sacrifice a creature.
Pyrrhic Blast deals damage equal to the sacrificed creature's power to any target. Draw a card.

Excavation Explosion

Excavation Explosion deals 3 damage to any target. Create a tapped Powerstone token. (It's an artifact with "{T}: Add {C}. This mana can't be spent to cast a nonartifact spell.")

Meria's Outrider

Reach
Domain — When Meria's Outrider enters, it deals damage to each opponent equal to the number of basic land types among lands you control.

Lightning Strike

Lightning Strike deals 3 damage to any target.

Obliterating Bolt

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

Mishra's Foundry

{T}: Add {C}.
{2}: Mishra's Foundry becomes a 2/2 Assembly-Worker artifact creature until end of turn. It's still a land.
{1}, {T}: Target attacking Assembly-Worker gets +2/+2 until end of turn.