Cast any other instant and/or sorcery spell, or wait for an opponent to cast one.
Holding priority, cast Expansion by paying {U/R}{U/R}, copying the next instant or sorcery spell you cast with mana value four or less.
Cast Twincast by paying {U}{U}, targeting the instant or sorcery spell cast in step 1.
The delayed trigger from Expansion triggers, copying Twincast, with the copy targeting the original Twincast.
Resolve the copy of Twincast, copying Twincast, with the copy targeting the original Twincast.
Repeat step 5.

Infinite magecraft triggers

Expansion // Explosion

Twincast

Cast any instant or sorcery with mana value 4 or less by paying its mana cost.
Holding priority, activate Pyromancer's Goggles by tapping it, adding {R}.
Cast Expansion by paying its mana cost, targeting the instant or sorcery cast in step 1.
Pyromancer's Goggles triggers, copying Expansion, with the copy targeting the original Expansion.
Resolve the copy of Expansion, creating a copy of Expansion targeting the original Expansion.
Repeat step 5.

Pyromancer's Goggles

Cast the additional sorcery by paying its mana cost.
Alania triggers; choose not to have an opponent draw a card.
Holding priority, cast Expansion by paying {U/R}{U/R}, targeting the additional sorcery.
Alania triggers, causing an opponent to draw a card and you to copy Expansion, with the copy targeting the original Expansion.
Resolve the copy of Expansion, copying the original Expansion, with the copy targeting the original Expansion.
Repeat step 5.

Alania, Divergent Storm

Cast the additional instant or sorcery by paying its mana cost.
If Adaptive Training Post had two charge counters on it, it triggers, putting a charge counter on it.
Holding priority, activate Adaptive Training Post by removing three charge counters from it, copying the next instant or sorcery spell you cast this turn.
Cast Expansion by paying its mana cost, targeting the spell cast in step 1.
Adaptive Training Post triggers, copying Expansion, with the copy targeting the original Expansion.
Resolve the copy of Expansion, copying the original Expansion, with the copy targeting the original Expansion.
Repeat step 5.

Adaptive Training Post

Cast any other instant and/or sorcery spell, or wait for an opponent to cast one.
Holding priority, cast Expansion by paying {U/R}{U/R}, copying the next instant or sorcery spell you cast with mana value four or less.
Cast Fork by paying {R}{R}, targeting the instant or sorcery spell cast in step 1.
The delayed trigger from Expansion triggers, copying Fork, with the copy targeting the original Fork.
Resolve the copy of Fork, copying Fork, with the copy targeting the original Fork.
Repeat step 5.

Fork

Cast an instant or sorcery spell, or wait for an opponent to cast one.
Holding priority, cast Expansion by paying {U/R}{U/R}, targeting the spell.
Activate Rootha by paying {2} and returning it to your hand, copying Expansion, with the copy targeting the original Expansion.
Resolve the copy of Expansion, copying Expansion, targeting the original Expansion.
Repeat step 4.

Rootha, Mercurial Artist

Cast Arcbond by paying {2}{R}, targeting Bloodthirsty Conqueror.
Holding priority, cast Expansion by paying its mana cost, copying Arcbond, with the copy targeting another indestructible creature you control.
Resolve both Arcbonds.
Deal damage to Bloodthirsty Conqueror.
Arbond triggers, dealing that much damage to each player and each other creature.
Bloodthirsty Conqueror triggers for each opponent dealt damage, and Arcbond triggers due to the other indestructible creature being dealt damage.
Resolve all Bloodthirsty Conqueror triggers, causing you to gain life.
Resolve the Arcbond trigger, dealing that much damage to each player and each other creature.
Bloodthirsty Conqueror triggers for each opponent dealt damage, and Arcbond triggers due to Bloodthirsty Conqueror being dealt damage.
Resolve all Bloodthirsty Conqueror triggers, causing you to gain life.
Resolve the Arcbond trigger, dealing that much damage to each player and each other creature.
Repeat form step 6.

Infinite damage

Infinite lifegain triggers

Infinite lifegain

Bloodthirsty Conqueror

Arcbond

Cast Twinflame by paying {3}{R}{R}, targeting any two creatures.
Holding priority, cast Expansion by paying its mana cost, copying Twinflame, with the copy targeting Priest of Urabrask and Pinnacle Monk.
Resolve the copy of Twinflame, creating a token copy of Priest of Urabrask and Pinnacle Monk with haste.
When the Priest of Urabrask and Pinnacle Monk tokens enter, they trigger.
Resolve the Priest of Urabrask trigger, adding {R}{R}{R}.
Resolve the Pinnacle Monk trigger, returning Expansion from your graveyard to your hand.
Repeat from step 2.

Combos with "Expansion // Explosion"