You have another instant and/or sorcery card in hand that can be cast using four or less colored mana.
You have enough mana to cast the additional instant or sorcery.
Steps
Cast any other instant or sorcery spell by paying its mana cost.
Swarm Intelligence and
Storm-Kiln Artist trigger.
Resolve the
Storm-Kiln Artist trigger, creating a Treasure artifact token.
Resolve the
Swarm Intelligence trigger, copying the spell.
Storm-Kiln Artist triggers, creating a Treasure artifact token.
Resolve the copy of the instant or sorcery.
Holding priority, activate the Treasures by tapping and sacrificing them, adding ({U} magic symbol) ({U} magic symbol) .
Cast
Narset's Reversal by paying ({U} magic symbol) ({U} magic symbol) , targeting the spell cast in step 1.
Swarm Intelligence and
Storm-Kiln Artist trigger.
Resolve the
Storm-Kiln Artist trigger, creating a Treasure artifact token.
Resolve the
Swarm Intelligence trigger, copying
Narset's Reversal, with the copy targeting the original
Narset's Reversal.
Storm-Kiln Artist triggers, creating a Treasure artifact token.
Resolve the copy of
Narset's Reversal, copying
Narset's Reversal with the copy targeting the spell cast in step 1, and then returning the original
Narset's Reversal to your hand.
Storm-Kiln Artist triggers, creating a Treasure artifact token.
Resolve the
Narset's Reversal copy, copying the spell it is targeting and returning the original spell to your hand.
Storm-Kiln Artist triggers, creating a Treasure artifact token.
Resolve the copy of the spell.
Activate any number of Treasures by tapping and sacrificing them, adding enough mana to cast the additional instant or sorcery.
Repeat.
If the additional spell can be cast for less than four mana, this combo nets infinite mana, which may be used to repeat this combo targeting any other instant and/or sorcery card in your hand and/or on the stack.
Results
Infinite colored mana.
Infinite copies of any instants and/or sorceries on the stack.