Cast any other instant or sorcery by paying its mana cost.
Holding priority, cast Return the Favor by paying its mana cost, targeting the instant or sorcery cast in step 1.
Return the Favor's storm ability triggers, creating at least one copy of Return the Favor targeting the original Return the Favor.
Resolve a copy of Return the Favor, copying Return the Favor targeting the original Return the Favor.
Repeat step 4.

Infinite magecraft triggers

Prismari, the Inspiration

Return the Favor

Cast any spell by paying its mana cost.
Holding priority, cast Unsubstantiate by paying its mana cost, targeting the spell cast in step 1.
Unsubstantiate's storm ability and Storm-Kiln Artist trigger.
Resolve the Storm-Kiln Artist trigger, creating a Treasure token.
Resolve the Unsubstantiate trigger, copying it for each spell cast before it this turn. Choose to have each copy target the original Unsubstantiate.
Storm-Kiln Artist triggers for each copy generated, creating that many Treasure tokens.
Resolve the first Unsubstantiate copy, returning the original Unsubstantiate to your hand.
All other copies of Unsubstantiate fizzle due to having no legal target.
Activate two Treasures by tapping and sacrificing them, adding {1}{U}.
Repeat from step 2.

Infinite artifact ETB

Infinite artifact LTB

Infinite artifact sacrifice triggers

Infinite artifact tokens

Infinite Treasure tokens

Infinite colored mana

Infinite storm count

Storm-Kiln Artist

Unsubstantiate

Cast a copy of Maestro's Gift by paying {3}{U}{R}, targeting Inspired Skypainter.
Maestro's Gift's storm ability triggers, copying it for each spell cast before it this turn. Choose to have each copy target Prismari.
Resolve the first copy of Maestro's Gift targeting Prismari, creating a token copy of Prismari with haste.
Repeat step 3 for each remaining copy of Maestro's Gift that targets Prismari.
Resolve the final copy of Maestro's Gift, creating a token copy of Inspired Skypainter with haste. It'll enter prepared due to its static effect.
Cast a copy of Maestro's Gift by paying {3}{U}{R}, targeting Inspired Skypainter.
Maestro's Gift will have a storm ability for each Prismari you control, and each storm ability will trigger.
Resolve the first storm trigger, copying Maestro's Gift for each spell cast before it this turn. Choose to have each copy target Prismari.
Repeat step 3 for each copy created in step 8.
Repeat steps 8 and 9 for each remaining storm trigger from step 7.
Repeat from step 5 as mana allows.

Near-infinite creature ETB

Near-infinite creature tokens with haste

Inspired Skypainter // Maestro's Gift

Sakashima of a Thousand Faces

Cast Bond of Insight by paying {3}{U}.
Grandmother Goby and Prismari trigger.
Resolve the Grandmother Goby trigger, countering Bond of Inisght and creating four 1/1 Merfolk creature tokens.
Resolve the Prismari trigger, copying Bond of Insight a number of times.
Resolve the first copy of Bond of Insight, causing each player to mill four cards and then returning the original Bond of Insight and up to one other instant or sorcery from your graveyard to your hand.
Repeat step 5 for other Bond of Insight copies as appropriate.
Activate Phyrexian Altar four times by sacrificing the four Merfolk tokens, adding {3}{U}.
Repeat.

Infinite creature ETB

Infinite creature LTB

Infinite creature sacrifice triggers

Infinite death triggers

Infinite mill

Infinite self-mill

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

Grandmother Goby

Phyrexian Altar

Bond of Insight

Combos with "Prismari, the Inspiration"