Cast Star of Extinction by paying {5}{R}{R}, destroying target land and dealing 20 damage to each creature and planeswalker.
Wrathful Red Dragon triggers for each Dragon you control.
Resolve the first Wrathful Red Dragon trigger, dealing 20 damage to any non-Dragon target.
Repeat step 3 for each remaining trigger.

Near-infinite damage

Wrathful Red Dragon

Star of Extinction

Declare any creature as an attacker. Dawnsire triggers, dealing 100 damage to  Wrathful Red Dragon.
Wrathful Red Dragon triggers, dealing 100 damage to any target that isn't a Dragon

Near-infinite damage to one opponent

Dawnsire, Sunstar Dreadnought

Cast Fire Covenant by {1}{B}{R} and paying an amount of life equal to an opponent's life total, dealing that much damage to Wrathful Red Dragon.
Wrathful Red Dragon triggers, dealing that much damage to the opponent.

Fire Covenant

Cause Wrathful Red Dragon to take damage by any method.
Wrathful Red Dragon triggers, dealing damage to an opponent.
Guilty Conscience triggers, dealing damage to Wrathful Red Dragon.
Repeat from step 2.

Infinite damage

Card that gives indestructible

Guilty Conscience

Deal damage to Wrathful Red Dragon.
Wrathful Red Dragon and Repercussion trigger.
Resolve the Wrathful Red Dragon trigger, dealing damage to an applicable target.
Resolve the Repercussion trigger, dealing damage to Wrathful Red Dragon instead of you due to Pariah's Shield.
Repeat from step 2.

Repercussion

Pariah's Shield

Cast Volcano Hellion by paying {2}{R}{R}.
When Volcano Hellion enters, it triggers, dealing an arbitarily large amount of damage to you and a creature. The damage that would be dealt to you is dealt to Wrathful Red Dragon instead due to Pariah.
Wrathful Red Dragon triggers, dealing an arbitrarily large amount of damage to an applicable target.

Infinite damage to one opponent

Volcano Hellion

Pariah

Cast Wheel of Misfortune by paying {2}{R}, choosing an arbitrarily large number and having Wheel of Misfortune deal that much damage to Wrathful Red Dragon instead of you due to Pariah's Shield if you chose the largest number.
Wrathful Red Dragon triggers, dealing that much damage to an applicable target.

Wheel of Misfortune

Deal noncombat damage to Smaug.
Smaug and Wrathful Red Dragon trigger.
Resolve the Smaug trigger, creating at least one Treasure token.
Resolve the Wrathful Red Dragon trigger, causing Smaug to deal damage to any non-Dragon target.
Guilty Conscience triggers, dealing damage to Smaug.
Repeat from step 2.

Infinite Treasure tokens

Infinite artifact ETB

Infinite artifact LTB

Infinite artifact sacrifice triggers

Infinite artifact tokens

Infinite colored mana

Smaug the Impenetrable

Earthbend a basic land you control.
Cast Legolas's Quick Reflexes by paying {G}, targeting the earthbent land.
Activate Earthcraft by tapping the earthbent land, targeting the earthbent land.
The land triggers, causing it to deal damage equal to its power to Wrathful Red Dragon.
Wrathful Red Dragon triggers, dealing that much damage to an applicable target.
Resolve the Earthcraft trigger, untapping the earthbent land.
Repeat from step 3.

Combos with "Wrathful Red Dragon"