Ash Zealot

First strike, haste
Whenever a player casts a spell from a graveyard, Ash Zealot deals 3 damage to that player.

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."

Hidden Volcano

Hidden Volcano enters tapped.
{T}: Add {R}.
{4}{R}, {T}, Sacrifice Hidden Volcano: Discover 4. Activate only as a sorcery. (Exile cards from the top of your library until you exile a nonland card with mana value 4 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.)

Darksteel Citadel

Refraction Elemental

Ward—Pay 2 life.
Whenever you cast a spell, Refraction Elemental deals 2 damage to each opponent.

Invasion of Karsus

(As a Siege enters, choose an opponent to protect it. You and others can attack it. When it's defeated, exile it, then cast it transformed.)
When Invasion of Karsus enters, it deals 3 damage to each creature and each planeswalker.

Invasion of Karsus // Refraction Elemental

Cascading Cataracts

Indestructible
{T}: Add {C}.
{5}, {T}: Add five mana in any combination of colors.

End the Festivities

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

Wild Slash

Ferocious — If you control a creature with power 4 or greater, damage can't be prevented this turn.
Wild Slash deals 2 damage to any target.

Fanatic of Mogis

When Fanatic of Mogis enters, it deals damage to each opponent equal to your devotion to red. (Each {R} in the mana costs of permanents you control counts toward your devotion to red.)

Furnace Punisher

Menace
At the beginning of each player's upkeep, Furnace Punisher deals 2 damage to that player unless they control two or more basic lands.

Monastery Swiftspear

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

Cleansing Wildfire

Destroy target land. Its controller may search their library for a basic land card, put it onto the battlefield tapped, then shuffle.
Draw a card.

Pit of Offerings

Pit of Offerings enters tapped.
When Pit of Offerings enters, exile up to three target cards from graveyards.
{T}: Add {C}.
{T}: Add one mana of any of the exiled cards' colors.

Scytheclaw Raptor

Whenever a player casts a spell, if it's not their turn, Scytheclaw Raptor deals 4 damage to them.