Cast Chain Lightning by paying {R}, dealing 3 damage to Smaug, Then, choose to pay {R}{R} to copy Chain Lightning, with the copy targeting Smaug.
Smaug triggers, creating three Treasure tokens.
Holding priority, activate two Treasures by tapping and sacrificing them, adding {R}{R}.
Resolve Chain Lightning, dealing 3 damage to Smaug, Then, choose to pay {R}{R} to copy Chain Lightning, with the copy targeting Smaug.
Repeat from step 2.

Infinite Treasure tokens

Infinite colored mana

Infinite magecraft triggers

Infinite artifact ETB

Infinite artifact LTB

Infinite artifact sacrifice triggers

Infinite artifact tokens

Smaug the Impenetrable

Chain Lightning

Cast Cursed Mirror by paying {2}{R}, choosing to have it enter the battlefield as a copy of Storm-Kiln Artist until end of turn.
Cast Chain Lightning by paying {R}, targeting Brash Taunter.
Storm-Kiln Artist and Cursed Mirror each trigger, creating two Treasure tokens.
Activate both Treasure tokens by tapping and sacrificing them, adding {R}{R}.
Resolve Chain Lightning, dealing 3 damage to Brash Taunter, and causing you to pay {R}{R} to copy Chain Lightning, targeting Brash Taunter.
Brash Taunter, Storm-Kiln Artist, and Cursed Mirror each trigger.
Resolve the Brash Taunter trigger, dealing 3 damage to an opponent.
Resolve the Storm-Kiln Artist and Cursed Mirror triggers, creating two Treasure tokens.
Repeat from step 4.

Infinite damage

Brash Taunter

Storm-Kiln Artist

Cursed Mirror

Cast Chain Lightning by paying {R}, dealing 3 damage to Raphael and then causing you to pay {R}{R} to copy Chain Lightning, with the copy targeting Raphael.
Raphael triggers, adding {R}{R}{R}.
Resolve the Chain Lightning copy, dealing 3 damage to Raphael and then causing you to pay {R}{R} to copy Chain Lightning, with the copy targeting Raphael.
Repeat from step 2.

Infinite red mana

Raphael, Ninja Destroyer

Cast Chain Lightning by paying {R}, targeting Brash Taunter.
Storm-Kiln Artist triggers, creating a Treasure token.
Activate the Treasure token by tapping and sacrificing it, adding {R}{R}.
Resolve Chain Lightning, dealing 3 damage to Brash Taunter, and causing you to pay {R}{R} to copy Chain Lightning, targeting Brash Taunter.
Brash Taunter and Storm-Kiln Artist each trigger.
Resolve the Brash Taunter trigger, dealing 3 damage to an opponent.
Resolve the Storm-Kiln Artist trigger, creating a Treasure token.
Repeat from step 3.

Goldspan Dragon

Cast Chain Lightning by paying {R}, targeting Brash Taunter.
Storm-Kiln Artist triggers, creating two Treasure tokens.
Activate both Treasure tokens by tapping and sacrificing them, adding {R}{R}.
Resolve Chain Lightning, dealing 3 damage to Brash Taunter, and causing you to pay {R}{R} to copy Chain Lightning, targeting Brash Taunter.
Brash Taunter and Storm-Kiln Artist each trigger.
Resolve the Brash Taunter trigger, dealing 3 damage to an opponent.
Resolve the Storm-Kiln Artist trigger, creating two Treasure tokens.
Repeat from step 3.

Xorn

Activate Mirage Mirror by paying {2}, causing it to become a copy of Storm-Kiln Artist until end of turn.
Cast Chain Lightning by paying {R}, targeting Brash Taunter.
Storm-Kiln Artist and Mirage Mirror each trigger, creating two Treasure tokens.
Activate both Treasure tokens by tapping and sacrificing them, adding {R}{R}.
Resolve Chain Lightning, dealing 3 damage to Brash Taunter, and causing you to pay {R}{R} to copy Chain Lightning, targeting Brash Taunter.
Brash Taunter, Storm-Kiln Artist, and Mirage Mirror each trigger.
Resolve the Brash Taunter trigger, dealing 3 damage to an opponent.
Resolve the Storm-Kiln Artist and Mirage Mirror triggers, creating two Treasure tokens.
Repeat from step 4.

Mirage Mirror

Jolene, the Plunder Queen

Cast Chain Lightning by paying {R}, targeting Crystalline Crawler.
Resolve Chain Lightning, putting three +1/+1 counters on Crystalline Crawler due to Vigor and choosing to pay {R}{R} to create a copy of Chain Lightning targeting Crystalline Crawler.
Holding priority, activate Crystalline Crawler's first ability twice by removing two +1/+1 counters from it, adding {R}{R}.
Repeat from step 2.

Combos with "Chain Lightning"