Cast any instant or sorcery by paying its mana cost.
Holding priority, cast Insidious Will by paying its mana cost, targeting the instant or sorcery cast in step 1.
Cast Narset's Reversal by paying {U}{U}, copying Insidious Will targeting the spell cast in step 1 and returning the original Insidious Will to your hand.
Cast Insidious Will by paying its mana cost, copying the copy of Insidious Will, targeting the copy of Insidious Will.
Resolve the copy of Insidious Will, creating a copy of Insidious Will targeting the copy of Insidious Will.
Repeat step 5.

Infinite magecraft triggers

Narset's Reversal

Insidious Will

Cast any sorcery by paying its mana cost.
Holding priority, cast Insidious Will by paying its mana cost.
Kalamax's first and second abilities trigger.
Resolve the first ability, creating a copy of Insidious Will and choosing to copy the original Insidious Will.
Resolve the second ability, putting a +1/+1 counter on Kalamax.
Resolve the Insidious Will copy, creating a copy of Insidious Will.
Kalamax's second ability triggers, putting a +1/+1 counter on itself.
Repeat from step 6 any number of times.

Infinite +1/+1 counters on a creature

Kalamax, the Stormsire

Cast the additional sorcery by paying its mana cost.
Alania triggers; choose not to have an opponent draw a card.
Holding priority, cast Insidious Will by paying {2}{U}{U}, targeting the additional sorcery.
Alania triggers, causing an opponent to draw a card and you to copy Insidious Will, with the copy targeting the original Insidious Will.
Resolve the copy of Insidious Will, copying the original Insidious Will, with the copy targeting the original Insidious Will.
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 Insidious Will by paying its mana cost, targeting the spell cast in step 1.
Adaptive Training Post triggers, copying Insidious Will, with the copy targeting the original Insidious Will.
Resolve the copy of Insidious Will, copying the original Insidious Will, with the copy targeting the original Insidious Will.
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 Dual Strike by paying {R}{R}, copying the next instant or sorcery spell you cast with mana value four or less.
Cast Insidious Will by paying {2}{U}{U}, targeting the instant or sorcery spell cast in step 1.
Dual Strike triggers, copying Insidious Will, with the copy targeting the original Insidious Will.
Resolve the copy of Insidious Will, copying Insidious Will, with the copy targeting the original Insidious Will.
Repeat step 5.

Dual Strike

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

Prismari, the Inspiration

Cast Gravitic Punch by paying its mana cost, targeting Kalamax.
Holding priority, cast Insidious Will by paying its mana cost, targeting Gravitic Punch.
Kalamax's first and second abilities trigger.
Resolve the first ability, creating a copy of Insidious Will targeting the original Insidious Will.
Resolve the second ability, putting a +1/+1 counter on Kalamax.
Resolve the Insidious Will copy, creating a copy of Insidious Will, targeting the original Insidious Will.
Kalamax's second ability triggers, putting a +1/+1 counter on itself.
Repeat from step 6 any number of times.
Once you have an arbitrarily large Kalamax, have the final Insidious Will copy target Gravitic Punch. This'll create two copies of Gravitic Punch in addition to the original Gravitic Punch.
Resolve all Gravitic Punches, dealing infinite damage to each of up to three opponents.

Infinite damage

Gravitic Punch

Cast Reality Spasm by paying at least {3}{U}{U}, targeting at least three permanents and choosing the untap mode.
Holding priority, cast Insidious Will by paying its mana cost, copying Reality Spasm, targeting at least three permanents.
Holding priority, activate at least two mana-producing permanents you control by tapping them, adding at least {1}{U}.
Activate Errant by paying {1}{U} and tapping it, copying the Reality Spasm copy, targeting Errant and at least two mana-producing permanents you control.
Resolve the copy of Reality Spasm from step 3, untapping Errant and at least two mana-producing permanents you control.
Repeat from step 3.

Infinite mana permanents you control can produce

Errant, Street Artist

Reality Spasm

Cast Arcbond by paying {2}{R}, targeting Bloodthirsty Conqueror.
Holding priority, cast Insidious Will 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.

Combos with "Insidious Will"