Blazing Sunsteel

Equipped creature gets +1/+0 for each opponent you have.
Whenever equipped creature is dealt damage, it deals that much damage to any target.
Equip {4}

Goblin Medics

Whenever this creature becomes tapped, it deals 1 damage to any target.

Barbflare Gremlin

First strike, haste
Whenever a player taps a land for mana, if this creature is tapped, that player adds one mana of any type that land produced. Then that land deals 1 damage to that player.

Akoum Hellkite

Flying
Landfall — Whenever a land you control enters, this creature deals 1 damage to any target. If that land is a Mountain, this creature deals 2 damage instead.

Barrage of Expendables

{R}, Sacrifice a creature: This enchantment deals 1 damage to any target.

Balduvian Trading Post

If this land would enter, sacrifice an untapped Mountain instead. If you do, put this land onto the battlefield. If you don't, put it into its owner's graveyard.
{T}: Add {C}{R}.
{1}, {T}: This land deals 1 damage to target attacking creature.

Barbed Field

Enchant land
Enchanted land has "{T}: This land deals 1 damage to any target."

Aria of Flame

When this enchantment enters, each opponent gains 10 life.
Whenever you cast an instant or sorcery spell, put a verse counter on this enchantment, then it deals damage equal to the number of verse counters on it to target player or planeswalker.

Aether Sting

Whenever an opponent casts a creature spell, this enchantment deals 1 damage to that player.

Blasting Station

{T}, Sacrifice a creature: This artifact deals 1 damage to any target.
Whenever a creature enters, you may untap this artifact.

Angry Rabble

Trample
Whenever you cast a spell with mana value 4 or greater, this creature deals 1 damage to each opponent.
{5}{R}: Put two +1/+1 counters on this creature. Activate only as a sorcery.

Ballista Charger

Whenever this Vehicle attacks, it deals 1 damage to any target.
Crew 3 (Tap any number of creatures you control with total power 3 or more: This Vehicle becomes an artifact creature until end of turn.)

Magic Missile

This spell can't be countered.
Magic Missile deals 3 damage divided as you choose among one, two, or three targets.

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 deals 2 damage to that permanent or player.

Barbed Wire

At the beginning of each player's upkeep, this artifact deals 1 damage to that player.
{2}: Prevent the next 1 damage that would be dealt by this artifact this turn.

Ballista Wielder

{2}{R}: This creature deals 1 damage to any target. A creature dealt damage this way can't block this turn.
Nightbound (If a player casts at least two spells during their own turn, it becomes day next turn.)

Ballista Watcher

{2}{R}, {T}: This creature deals 1 damage to any target.
Daybound (If a player casts no spells during their own turn, it becomes night next turn.)

Ballista Watcher // Ballista Wielder

Mysidian Elder

When this creature enters, create a 0/1 black Wizard creature token with "Whenever you cast a noncreature spell, this token deals 1 damage to each opponent."

Aggravate

Aggravate deals 1 damage to each creature target player controls. Each creature dealt damage this way attacks this turn if able.

Battle Strain

Whenever a creature blocks, this enchantment deals 1 damage to that creature's controller.