Impact Tremors

Whenever a creature you control enters, this enchantment deals 1 damage to each opponent.

Aether Sting

Whenever an opponent casts a creature spell, Aether Sting deals 1 damage to that player.

Boggart Shenanigans

Whenever another Goblin you control is put into a graveyard from the battlefield, you may have Boggart Shenanigans deal 1 damage to target player or planeswalker.

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.

Hissing Iguanar

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

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.