Cemetery Gatekeeper

First strike
When Cemetery Gatekeeper enters, exile a card from a graveyard.
Whenever a player plays a land or casts a spell, if it shares a card type with the exiled card, Cemetery Gatekeeper deals 2 damage to that player.

Wheel of Misfortune

Each player secretly chooses a number 0 or greater, then all players reveal those numbers simultaneously and determine the highest and lowest numbers revealed this way. Wheel of Misfortune deals damage equal to the highest number to each player who chose that number. Each player who didn't choose the lowest number discards their hand, then draws seven cards.

Volcano Hellion

Volcano Hellion has echo {X}, where X is your life total. (At the beginning of your upkeep, if this came under your control since the beginning of your last upkeep, sacrifice it unless you pay its echo cost.)
When Volcano Hellion enters, it deals an amount of damage of your choice to you and target creature. The damage can't be prevented.

Spellshock

Whenever a player casts a spell, Spellshock deals 2 damage to that player.

Auntie Blyte, Bad Influence

Flying
Whenever a source you control deals damage to you, put that many +1/+1 counters on Auntie Blyte, Bad Influence.
{1}{R}, {T}, Remove X +1/+1 counters from Auntie Blyte: It deals X damage to any target.

Descent into Avernus

At the beginning of your upkeep, put two descent counters on Descent into Avernus. Then each player creates X Treasure tokens and Descent into Avernus deals X damage to each player, where X is the number of descent counters on Descent into Avernus.

Barbarian Ring

{T}: Add {R}. Barbarian Ring deals 1 damage to you.
Threshold — {R}, {T}, Sacrifice Barbarian Ring: It deals 2 damage to any target. Activate only if seven or more cards are in your graveyard.

Eidolon of the Great Revel

Whenever a player casts a spell with mana value 3 or less, Eidolon of the Great Revel deals 2 damage to that player.

Flame Rift

Flame Rift deals 4 damage to each player.

Sunspine Lynx

Players can't gain life.
Damage can't be prevented.
When Sunspine Lynx enters, it deals damage to each player equal to the number of nonbasic lands that player controls.

Manabarbs

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

Heartless Hidetsugu

{T}: Heartless Hidetsugu deals damage to each player equal to half that player's life total, rounded down.

Orcish Artillery

{T}: Orcish Artillery deals 2 damage to any target and 3 damage to you.

Blasphemous Act

This spell costs {1} less to cast for each creature on the battlefield.
Blasphemous Act deals 13 damage to each creature.

Goblin Artillery

{T}: Goblin Artillery deals 2 damage to any target and 3 damage to you.

Rug of Smothering

Flying
Whenever a player casts a spell, they lose 1 life for each spell they've cast this turn.

Fireslinger

{T}: Fireslinger deals 1 damage to any target and 1 damage to you.

Torbran, Thane of Red Fell

If a red source you control would deal damage to an opponent or a permanent an opponent controls, it deals that much damage plus 2 instead.

Jackal Pup

Whenever Jackal Pup is dealt damage, it deals that much damage to you.

Coalhauler Swine

Whenever Coalhauler Swine is dealt damage, it deals that much damage to each player.

Spear Spewer

Defender
{T}: Spear Spewer deals 1 damage to each player.

Orcish Cannoneers

{T}: Orcish Cannoneers deals 2 damage to any target and 3 damage to you.

Magebane Lizard

Whenever a player casts a noncreature spell, Magebane Lizard deals damage to that player equal to the number of noncreature spells they've cast this turn.