A Unison Chance is triggered when you or an ally activates a Unison Skill.
Tap the UNISON button to activate a Unison Skill. Select an equipped Monster to activate their Unison Skill. Different Monsters activate different Skills.

The order in which the effects are activated is as written in the effect description for the equipped Monster.
However, for skills that deal multiple physical/magic attacks, the attacks are dealt after all other effects have been activated.

[Added 3/16/2023]
Below is an example of the order effects are activated for the following Unison effect.

▼Unison Effect
-Target: all enemies. Ability Power 400. Deals physical fire damage 5 times with a success value of 100.
└Ability Power boosted by 10 for each increase in Skill level.
-Target: all enemies. Applies status ailment A.
-Target: all enemies. Applies debuff A.
-Target: all enemies. Applies status ailment B.
-Target: all allies. Applies buff A.

▼Activation Order
1. Attempt to apply status ailment A
2. Apply debuff A
3. Attempt to apply status ailment B
4. Apply buff A
5. Ability Power 400 physical attack
6. Ability Power 400 physical attack
7. Ability Power 400 physical attack
8. Ability Power 400 physical attack
9. Ability Power 400 physical attack

You can summon a Great Spirit by summoning a Monster with the same element as a Unison Attack performed by an ally.
Summoning a Great Spirit can quickly turn the tide of battle to your favor, so try to work together with your allies to seize this opportunity whenever possible.

The more Great Spirits of the same element, the stronger their attacks will be.
Great Spirit Abilities can also change depending on the combination of Unison Attack elements.
The total of certain stat values belonging to all players participating in the Great Spirit Attack affects the attack's power, so you'll do more damage with more players working together.

[ Fire Great Spirit ]
Apocalypse Lv 1 : Ability Power 180. Damages all enemies with physical fire damage.
Apocalypse Lv 2 : Ability Power 180. Damages all enemies with physical fire damage.
Apocalypse Lv 3 : Ability Power 180. Damages all enemies with physical fire damage.
Apocalypse Lv 4 : Ability Power 180. Damages all enemies with physical fire damage.

[ Water Great Spirit ]
Deep Tempest Lv 1 : Ability Power 120. Damages all enemies with physical water damage. Recovers 20% of max HP for all allies. Recovers 5% of max HP for all allies every 5 seconds for 20 seconds.
Deep Tempest Lv 2 : Ability Power 120. Damages all enemies with physical water damage. Recovers 30% of max HP for all allies. Recovers 5% of max HP for all allies every 5 seconds for 20 seconds.
Deep Tempest Lv 3 : Ability Power 120. Damages all enemies with physical water damage. Recovers 40% of max HP for all allies. Recovers 5% of max HP for all allies every 5 seconds for 20 seconds.
Deep Tempest Lv 4 : Ability Power 120. Damages all enemies with physical water damage. Recovers 50% of max HP for all allies. Recovers 5% of max HP for all allies every 5 seconds for 20 seconds.

[ Wind Great Spirit ]
Heavenly Storm Lv 1 : Ability Power 130. Damages all enemies with physical wind damage. Increases the stats of all allies by 10% for 60 seconds.
Heavenly Storm Lv 2 : Ability Power 130. Damages all enemies with physical wind damage. Increases the stats of all allies by 20% for 60 seconds.
Heavenly Storm Lv 3 : Ability Power 130. Damages all enemies with physical wind damage. Increases the stats of all allies by 30% for 60 seconds.
Heavenly Storm Lv 4 : Ability Power 130. Damages all enemies with physical wind damage. Increases the stats of all allies by 40% for 60 seconds.

[ Light Great Spirit ]
Sacred Ray Lv 1 : Ability Power 180. Damages all enemies with physical light damage.
Sacred Ray Lv 2 : Ability Power 180. Damages all enemies with physical light damage.
Sacred Ray Lv 3 : Ability Power 180. Damages all enemies with physical light damage.
Sacred Ray Lv 4 : Ability Power 180. Damages all enemies with physical light damage.

[ Dark Great Spirit ]
Hellcaller Lv 1 : Ability Power 130. Damages all enemies with magic dark damage. Decreases stats of all enemies by 10% for 60 seconds.
Hellcaller Lv 2 : Ability Power 130. Damages all enemies with magic dark damage. Decreases stats of all enemies by 20% for 60 seconds.
Hellcaller Lv 3 : Ability Power 130. Damages all enemies with magic dark damage. Decreases stats of all enemies by 30% for 60 seconds.
Hellcaller Lv 4 : Ability Power 130. Damages all enemies with magic dark damage. Decreases stats of all enemies by 40% for 60 seconds.

[ Star Great Spirit ]
Wheel of Fate Lv 1 : Ability Power 180. Damages all enemies with magic star damage. Removes buffs from all enemies.
Wheel of Fate Lv 2 : Ability Power 180. Damages all enemies with magic star damage. Removes buffs from all enemies. Removes debuffs from all allies.
Wheel of Fate Lv 3 : Ability Power 180. Damages all enemies with magic star damage. Casts Karma on all enemies. Removes debuffs from all allies.
Wheel of Fate Lv 4 : Ability Power 180. Damages all enemies with magic star damage. Casts Karma on all enemies. Casts Kismet on all allies.

[ Time Great Spirit ]
Haste Lv 1 : Ability Power 200. Damages all enemies with magic time damage. Increases the Cost recovery speed of all allies by 5 for 60 seconds. Increases the Unison gauge gains of all allies by 2 for 60 seconds.
Haste Lv 2 : Ability Power 200. Damages all enemies with magic time damage. Increases the Cost recovery speed of all allies by 10 for 60 seconds. Increases the Unison gauge gains of all allies by 3 for 60 seconds.
Haste Lv 3 : Ability Power 200. Damages all enemies with magic time damage. Increases the Cost recovery speed of all allies by 10 for 60 seconds. Increases the Unison gauge gains of all allies by 4 for 60 seconds.
Haste Lv 4 : Ability Power 200. Damages all enemies with magic time damage. Increases the Cost recovery speed of all allies by 10 for 60 seconds. Increases the Unison gauge gains of all allies by 5 for 60 seconds.