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.

Obosh, the Preypiercer

Companion — Your starting deck contains only cards with odd mana values and land cards. (If this card is your chosen companion, you may put it into your hand from outside the game for {3} as a sorcery.)
If a source you control with an odd mana value would deal damage to a permanent or player, it deals double that damage to that permanent or player instead.

The Lord of Pain

Menace
Your opponents can't gain life.
Whenever a player casts their first spell each turn, choose another target player. The Lord of Pain deals damage equal to that spell's mana value to the chosen player.

Rampaging Ferocidon

Menace
Players can't gain life.
Whenever another creature enters, this creature deals 1 damage to that creature's controller.

Manabarbs

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

Kederekt Parasite

Whenever an opponent draws a card, if you control a red permanent, you may have this creature deal 1 damage to that player.

Spellshock

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

Sulfuric Vortex

At the beginning of each player's upkeep, this enchantment deals 2 damage to that player.
If a player would gain life, that player gains no life instead.

Zo-Zu the Punisher

Whenever a land enters, Zo-Zu deals 2 damage to that land's controller.

Vial Smasher the Fierce

Whenever you cast your first spell each turn, choose an opponent at random. Vial Smasher deals damage equal to that spell's mana value to that player or a planeswalker that player controls.
Partner (You can have two commanders if both have partner.)

Repercussion

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