Spitemare

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

Reckless Rage

Reckless Rage deals 4 damage to target creature you don't control and 2 damage to target creature you control.

Sporeweb Weaver

Reach, hexproof from blue
Whenever Sporeweb Weaver is dealt damage, you gain 1 life and create a 1/1 green Saproling creature token.

Naya Charm

Choose one —
• Naya Charm deals 3 damage to target creature.
• Return target card from a graveyard to its owner's hand.
• Tap all creatures target player controls.

Wrathful Red Dragon

Flying
Whenever a Dragon you control is dealt damage, it deals that much damage to any target that isn't a Dragon.

Rite of Passage

Whenever a creature you control is dealt damage, put a +1/+1 counter on it. (It must survive the damage to get the counter.)

Needletooth Raptor

Enrage — Whenever Needletooth Raptor is dealt damage, it deals 5 damage to target creature an opponent controls.

Broodhatch Nantuko

Whenever Broodhatch Nantuko is dealt damage, you may create that many 1/1 green Insect creature tokens.
Morph {2}{G} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)

Ranging Raptors

Enrage — Whenever Ranging Raptors is dealt damage, you may search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Snapping Sailback

Flash
Enrage — Whenever Snapping Sailback is dealt damage, put a +1/+1 counter on it. (It must survive the damage to get the counter.)

Vrondiss, Rage of Ancients

Enrage — Whenever Vrondiss, Rage of Ancients is dealt damage, you may create a 5/4 red and green Dragon Spirit creature token with "When this creature deals damage, sacrifice it."
Whenever you roll one or more dice, you may have Vrondiss deal 1 damage to itself.

Phytohydra

If damage would be dealt to Phytohydra, put that many +1/+1 counters on it instead.

Cacophodon

Enrage — Whenever Cacophodon is dealt damage, untap target permanent.

Rile

Rile deals 1 damage to target creature you control. That creature gains trample until end of turn.
Draw a card.

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}

Trapjaw Tyrant

Enrage — Whenever Trapjaw Tyrant is dealt damage, exile target creature an opponent controls until Trapjaw Tyrant leaves the battlefield.

Silverclad Ferocidons

Enrage — Whenever Silverclad Ferocidons is dealt damage, each opponent sacrifices a permanent of their choice.

Siegehorn Ceratops

Enrage — Whenever Siegehorn Ceratops is dealt damage, put two +1/+1 counters on it. (It must survive the damage to get the counters.)

Arcbond

Choose target creature. Whenever that creature is dealt damage this turn, it deals that much damage to each other creature and each player.

Stuffy Doll

Indestructible
As Stuffy Doll enters, 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.

Hornet Nest

Defender (This creature can't attack.)
Whenever Hornet Nest is dealt damage, create that many 1/1 green Insect creature tokens with flying and deathtouch. (Any amount of damage a creature with deathtouch deals to a creature is enough to destroy it.)

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.

Hungering Hydra

Hungering Hydra enters with X +1/+1 counters on it.
Hungering Hydra can't be blocked by more than one creature.
Whenever Hungering Hydra is dealt damage, put that many +1/+1 counters on it. (It must survive the damage to get the counters.)

Polyraptor

Enrage — Whenever Polyraptor is dealt damage, create a token that's a copy of Polyraptor.

Apex Altisaur

When Apex Altisaur enters, it fights up to one target creature you don't control.
Enrage — Whenever Apex Altisaur is dealt damage, it fights up to one target creature you don't control.

Flumph

Defender, flying
Whenever Flumph is dealt damage, you and target opponent each draw a card.

Blasphemous Act

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

Howlpack Avenger

Whenever a permanent you control is dealt damage, Howlpack Avenger deals that much damage to any target.
{1}{R}: Howlpack Avenger gets +2/+0 until end of turn.
Nightbound (If a player casts at least two spells during their own turn, it becomes day next turn.)

Ill-Tempered Loner

Whenever Ill-Tempered Loner is dealt damage, it deals that much damage to any target.
{1}{R}: Ill-Tempered Loner gets +2/+0 until end of turn.
Daybound (If a player casts no spells during their own turn, it becomes night next turn.)

Ill-Tempered Loner // Howlpack Avenger

Phyrexian Vindicator

Flying
If damage would be dealt to Phyrexian Vindicator, prevent that damage. When damage is prevented this way, Phyrexian Vindicator deals that much damage to any other target.

Sprouting Phytohydra

Defender (This creature can't attack.)
Whenever Sprouting Phytohydra is dealt damage, you may create a token that's a copy of Sprouting Phytohydra.

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.