Cast any instant or sorcery spell.
Holding priority, cast Cooperate from your graveyard by paying {2}{U}.
Sevinne triggers, creating a copy of Cooperate, targeting Cooperate.
Resolve the copy of Cooperate, creating a copy of Cooperate, targeting Cooperate.
Repeat step 4.

Infinite magecraft triggers

Sevinne, the Chronoclasm

Refuse // Cooperate

Cast the additional sorcery by paying its mana cost.
Alania triggers; choose not to have an opponent draw a card.
Holding priority, cast Cooperate from your graveyard by paying {2}{U}, targeting the additional sorcery.
Alania triggers, causing an opponent to draw a card and you to copy Cooperate, with the copy targeting the original Cooperate.
Resolve the copy of Cooperate, copying the original Cooperate, with the copy targeting the original Cooperate.
Repeat step 5.

Alania, Divergent Storm

Cast the spell in your hand.
In response cast Refuse // Cooperate from your graveyard to copy it.
Sevinne, the Chronoclasm's ability triggers copying Refuse // Cooperate.
Copy the original Refuse // Cooperate.
Repeat.
For each copy made Ral, Storm Conduit will trigger dealing 1 damage to an opponent.

Infinite damage

Ral, Storm Conduit

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

Rootha, Mercurial Artist

Cast Chandra's Ignition by paying {3}{R}{R}.
Holding priority, cast Cooperate from your graveyard by paying {2}{U}.
Kalamax's first and second abilities trigger.
Resolve the first ability, creating a copy of Cooperate targeting Chanrda's Ignition.
Resolve the second ability, putting a +1/+1 counter on Kalamax.
Resolve the Cooperate copy, creating a copy of Cooperate.
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, resolve Chandra's Ignition, causing Kalamax to deal damage equal to its power to each other creature and each opponent.

Infinite +1/+1 counters on Kalamax

Kalamax, the Stormsire

Chandra's Ignition

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 Cooperate from your graveyard by paying its mana cost, targeting the spell cast in step 1.
Adaptive Training Post triggers, copying Cooperate, with the copy targeting the original Cooperate.
Resolve the copy of Cooperate, copying the original Cooperate, with the copy targeting the original Cooperate.
Repeat step 5.

Adaptive Training Post

Cast Reality Spasm by paying at least {3}{U}{U}, targeting at least three permanents and choosing the untap mode.
Holding priority, cast Cooperate from your graveyard 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

Infinite untap of permanents you control

Errant, Street Artist

Reality Spasm

Cast Arcbond by paying {2}{R}, targeting Bloodthirsty Conqueror.
Holding priority, cast Cooperate from your graveyard 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 "Refuse // Cooperate"