Truefire Captain

Mentor (Whenever this creature attacks, put a +1/+1 counter on target attacking creature with lesser power.)
Whenever Truefire Captain is dealt damage, it deals that much damage to target player.

Livewire Lash

Equipped creature gets +2/+0 and has "Whenever this creature becomes the target of a spell, this creature deals 2 damage to any target."
Equip {2}

Rip Apart

Choose one —
• Rip Apart deals 3 damage to target creature or planeswalker.
• Destroy target artifact or enchantment.

Spitemare

Whenever Spitemare is dealt damage, it deals that much damage to any target.

Stensia Uprising

At the beginning of your end step, create a 1/1 red Human creature token. Then if you control exactly thirteen permanents, you may sacrifice Stensia Uprising. When you do, it deals 7 damage to any target.

Brash Taunter

Indestructible
Whenever Brash Taunter is dealt damage, it deals that much damage to target opponent.
{2}{R}, {T}: Brash Taunter fights another target creature.

Guilty Conscience

Enchant creature
Whenever enchanted creature deals damage, Guilty Conscience deals that much damage to that creature.

Pariah

Enchant creature
All damage that would be dealt to you is dealt to enchanted creature instead.

Firesong and Sunspeaker

Red instant and sorcery spells you control have lifelink.
Whenever a white instant or sorcery spell causes you to gain life, Firesong and Sunspeaker deals 3 damage to target creature or player.

Lightning Helix

Lightning Helix deals 3 damage to any target and you gain 3 life.

Lightning Bolt

Lightning Bolt deals 3 damage to any target.

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 the battlefield, it deals an amount of damage of your choice to you and target creature. The damage can't be prevented.

Tower of Calamities

{8}, {T}: Tower of Calamities deals 12 damage to target creature.

General's Regalia

{3}: The next time a source of your choice would deal damage to you this turn, that damage is dealt to target creature you control instead.

Boros Reckoner

Whenever Boros Reckoner is dealt damage, it deals that much damage to any target.
{R/W}: Boros Reckoner gains first strike until end of turn.

Star of Extinction

Destroy target land. Star of Extinction deals 20 damage to each creature and each planeswalker.

Stuffy Doll

Indestructible
As Stuffy Doll enters the battlefield, choose a player.
Whenever Stuffy Doll is dealt damage, it deals that much damage to the chosen player.
{T}: Stuffy Doll deals 1 damage to itself.

Shivan Meteor

Shivan Meteor deals 13 damage to target creature.
Suspend 2—{1}{R}{R} (Rather than cast this card from your hand, you may pay {1}{R}{R} and exile it with two time counters on it. At the beginning of your upkeep, remove a time counter. When the last is removed, you may cast it without paying its mana cost.)

Fatal Attraction

Enchant creature
When Fatal Attraction enters the battlefield, it deals 2 damage to enchanted creature.
At the beginning of your upkeep, Fatal Attraction deals 4 damage to enchanted creature.

Chain Reaction

Chain Reaction deals X damage to each creature, where X is the number of creatures on the battlefield.