Roiling Vortex

At the beginning of each player's upkeep, this enchantment deals 1 damage to them.
Whenever a player casts a spell, if no mana was spent to cast that spell, this enchantment deals 5 damage to that player.
{R}: Your opponents can't gain life this turn.

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.")

Grapeshot

Grapeshot deals 1 damage to any target.
Storm (When you cast this spell, copy it for each spell cast before it this turn. You may choose new targets for the copies.)

Unruly Catapult

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

Neko-Te

Whenever equipped creature deals damage to a creature, tap that creature. That creature doesn't untap during its controller's untap step for as long as Neko-Te remains on the battlefield.
Whenever equipped creature deals damage to a player, that player loses 1 life.
Equip {2}

Scorching Winds

Cast this spell only during the declare attackers step and only if you've been attacked this step.
Scorching Winds deals 1 damage to each attacking creature.

Mass Diminish

Until your next turn, creatures target player controls have base power and toughness 1/1.
Flashback {3}{U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Eroded Canyon

This land enters tapped.
When this land enters, it deals 1 damage to target opponent.
{T}: Add {U} or {R}.

Repercussion

Whenever a creature is dealt damage, this enchantment deals that much damage to that creature's controller.

Flatline

Creatures your opponents control have base power and toughness 0/1 until end of turn.

Saheeli Rai

+1: Scry 1. Saheeli Rai deals 1 damage to each opponent.
−2: Create a token that's a copy of target artifact or creature you control, except it's an artifact in addition to its other types. That token gains haste. Exile it at the beginning of the next end step.
−7: Search your library for up to three artifact cards with different names, put them onto the battlefield, then shuffle.

End the Festivities

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

Goblin Chainwhirler

First strike
When this creature enters, it deals 1 damage to each opponent and each creature and planeswalker they control.

Mithril Coat

Flash
Indestructible
When Mithril Coat enters, attach it to target legendary creature you control.
Equipped creature has indestructible.
Equip {3}

Ferrous Lake

Thundering Falls

({T}: Add {U} or {R}.)
This land enters tapped.
When this land enters, surveil 1. (Look at the top card of your library. You may put it into your graveyard.)

Steam Clean

Return target nonland permanent to its owner's hand. (Then exile this card. You may cast the creature later from exile.)

Scalding Viper

Whenever an opponent casts a spell with mana value 3 or less, this creature deals 1 damage to that player.

Scalding Viper // Steam Clean

Tectonic Hazard

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

Stormcarved Coast

This land enters tapped unless you control two or more other lands.
{T}: Add {U} or {R}.

Kessig Flamebreather

Whenever you cast a noncreature spell, this creature deals 1 damage to each opponent.