Manabarbs

Whenever a player taps a land for mana, Manabarbs deals 1 damage to that player.

Firebrand Archer

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

Lava Dart

Lava Dart deals 1 damage to any target.
Flashback—Sacrifice a Mountain. (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Dance with Devils

Create two 1/1 red Devil creature tokens. They have "When this creature dies, it deals 1 damage to any target."

Shivan Hellkite

Flying (This creature can't be blocked except by creatures with flying or reach.)
{1}{R}: Shivan Hellkite deals 1 damage to any target.

Kessig Flamebreather

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

Lightning Cloud

Whenever a player casts a red spell, you may pay {R}. If you do, Lightning Cloud deals 1 damage to any target.

Caltrops

Whenever a creature attacks, Caltrops deals 1 damage to it.

Impact Resonance

Impact Resonance deals X damage divided as you choose among any number of target creatures, where X is the greatest amount of damage dealt by a source to a permanent or player this turn.

Chandra's Spitfire

Flying
Whenever an opponent is dealt noncombat damage, Chandra's Spitfire gets +3/+0 until end of turn.

Kyren Negotiations

Tap an untapped creature you control: Kyren Negotiations deals 1 damage to target player or planeswalker.

Burning Earth

Whenever a player taps a nonbasic land for mana, Burning Earth deals 1 damage to that player.

Ancient Hellkite

Flying
{R}: Ancient Hellkite deals 1 damage to target creature defending player controls. Activate only if Ancient Hellkite is attacking.

Culmination of Studies

Exile the top X cards of your library. For each land card exiled this way, create a Treasure token. For each blue card exiled this way, draw a card. For each red card exiled this way, Culmination of Studies deals 1 damage to each opponent.

Hissing Iguanar

Whenever another creature dies, you may have Hissing Iguanar deal 1 damage to target player or planeswalker.

Circle of Flame

Whenever a creature without flying attacks you or a planeswalker you control, Circle of Flame deals 1 damage to that creature.

Flameblade Angel

Flying
Whenever a source an opponent controls deals damage to you or a permanent you control, you may have Flameblade Angel deal 1 damage to that source's controller.

Ghyrson Starn, Kelermorph

Ward {2} (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {2}.)
Three Autostubs — Whenever another source you control deals exactly 1 damage to a permanent or player, Ghyrson Starn, Kelermorph deals 2 damage to that permanent or player.

Spiteful Prankster

During your turn, Spiteful Prankster has first strike.
Whenever another creature dies, Spiteful Prankster deals 1 damage to target player or planeswalker.

Devils' Playground

Create four 1/1 red Devil creature tokens. They have "When this creature dies, it deals 1 damage to any target."

Flame Jab

Flame Jab deals 1 damage to any target.
Retrace (You may cast this card from your graveyard by discarding a land card in addition to paying its other costs.)

Flame Fusillade

Until end of turn, permanents you control gain "{T}: This permanent deals 1 damage to any target."