Spellweaver Volute and Thousand-Year Storm on the battlefield.
Pull from Eternity and Turnabout in your graveyard.
Two additional instant cards in graveyard.
Spellweaver Volute attached to Turnabout.
You control lands that can tap to add at least ({6} magic symbol) ({U} magic symbol) ({U} magic symbol) .
({4} magic symbol) ({U} magic symbol) available.
Steps
Cast Petals of Insight by paying ({4} magic symbol) ({U} magic symbol) .
Thousand-Year Storm and Spellweaver Volute trigger.
Resolve Spellweaver Volute's trigger, casting a copy of Turnabout, exiling Turnabout, and attaching Spellweaver Volute to Pull from Eternity.
Thousand-Year Storm triggers, copying Turnabout for each other instant and sorcery spell you've cast before it this turn.
Activate your lands by tapping them to add mana.
Resolve a copy of Turnabout, untapping all lands you control.
Repeat the previous two steps for each remaining Turnabout on the stack, resulting in at least ({U} magic symbol) ({U} magic symbol) ({U} magic symbol) plus twelve generic mana available.
Resolve the remaining Thousand-Year Storm trigger, copying Petals of Insight for each other instant and sorcery spell you've cast before it this turn.
Resolve all non-card copies of Petals of Insight, drawing three cards for each one.
Resolve the original Petals of Insight, returning it to your hand.
Cast Petals of Insight by paying ({4} magic symbol) ({U} magic symbol) .
Thousand-Year Storm and Spellweaver Volute trigger.
Resolve Spellweaver Volute's trigger, casting a copy of Pull from Eternity, exiling Pull from Eternity, and attaching Spellweaver Volute to any instant card in your graveyard.
Thousand-Year Storm triggers, copying Pull from Eternity for each other instant and sorcery spell you've cast before it this turn.
Resolve all copies of Pull from Eternity, returning Pull from Eternity, Turnabout, and (if possible) any other instant card from exile to your graveyard.
Resolve the remaining Thousand-Year Storm trigger, copying Petals of Insight for each other instant and sorcery spell you've cast before it this turn.
Resolve all non-card copies of Petals of Insight, drawing three cards for each one.
Resolve the original Petals of Insight, returning it to your hand.
Cast Petals of Insight by paying ({4} magic symbol) ({U} magic symbol) .
Thousand-Year Storm and Spellweaver Volute trigger.
Resolve Spellweaver Volute's trigger, casting a copy of the instant it is attached to, exiling that instant card, and attaching Spellweaver Volute to Turnabout.
Thousand-Year Storm triggers, copying the instant for each other instant and sorcery spell you've cast before it this turn.
Resolve all copies of the instant.
Resolve the remaining Thousand-Year Storm trigger, copying Petals of Insight for each other instant or sorcery you've cast before it this turn.
Resolve all non-card copies of Petals of Insight, drawing three cards for each one.
Resolve the original Petals of Insight, returning it to your hand.
Repeat, choosing not to draw cards with Petals of Insight when needed to avoid losing the game.
Results
Cast any instant cards from your graveyard, your library, exile, and opponents' graveyards infinite times.
Infinite mana lands you control can produce.
Infinite storm count.
Infinite untap of artifacts, creatures, and lands.