Cast the other instant or sorcery by paying its mana cost.
Molten-Core Maestro triggers, putting a +1/+1 counter on it, and adding an amount of {R} equal to its power if the spell had mana value 5 or greater.
Holding priority, cast Reiterate with buyback by paying {4}{R}{R}, targeting the instant or sorcery.
Molten-Core Maestro triggers, putting a +1/+1 counter on it and adding an amount of {R} equal to its power.
Resolve Reiterate, copying the instant or sorcery and returning Reiterate to your hand.
Repeat from step 3.

Infinite +1/+1 counters on a creature

Infinite copies of the casted instant or sorcery

Infinite magecraft triggers

Infinite red mana

Infinite storm count

Molten-Core Maestro

Reiterate

Cast Searing Touch with buyback by paying {4}{R}
Molten-Core Maestro triggers, putting a +1/+1 counter on it and adding an amount of {R} equal to its power.
Resolve Searing Touch, dealing 1 damage to any target and returning it to your hand.
Repeat.

Infinite damage

Searing Touch

Cast Fanning the Flames with buyback by paying {3}{R}{R}
Molten-Core Maestro triggers, putting a +1/+1 counter on it and adding an amount of {R} equal to its power.
Resolve Fanning the Flames, returning it to your hand.
Repeat.

Fanning the Flames

Cast the copy of the spell from exile by paying its mana cost.
When you cast that spell, Molten-Core Maestro, Storm-Kiln Artist, and Displacer Kitten trigger.
Resolve the Displacer Kitten trigger, blinking Sanar, Unfinished Genius, which enters prepared.
Resolve the Molten-Core Maestro trigger, putting a +1/+1 counter on it and adding an amount of {R} equal to its power.
Resolve the Storm-Kiln Artist trigger, creating a Treasure token.
Activate the Treasure token by tapping and sacrificing it, adding the one non-red mana you need to cast the spell from step 1.
Resolve the spell from step 1.
Repeat.

Infinite artifact ETB

Infinite artifact LTB

Infinite creature ETB

Infinite creature LTB

Put all instant and sorcery cards from your library into your hand

Displacer Kitten

Storm-Kiln Artist

Sanar, Unfinished Genius // Wild Idea

Cast a copy of Maestro's Gift from exile by paying {3}{U}{R}.
When you cast that spell, Molten-Core Maestro triggers, putting a +1/+1 counter on itself and adding an amount of {R} equal to its power.
Maestro's Gift resolves, creating a copy of Inspired Skypainter who enters prepared and with haste.
If needed, activate Energy Refractor by paying {R}{R}, adding {U}
Repeat, adding an ever-increasing amount of {R} in step 2.

Infinite colored mana

Infinite copies of a specific creature with haste

Inspired Skypainter // Maestro's Gift

Energy Refractor

Combos with "Molten-Core Maestro"