Mog is a non-player character in Dissidia Final Fantasy Opera Omnia. He is a servant of the goddess, Materia. His main function is recruiting new characters into the playable roster and explaining the situation to them.
When Torsions begin to appear in the world created for the warriors' respite, Mog volunteers to investigate and help fix the problem. He senses warriors who bear the light and attempts to recruit them to the quest. Starting with Rem, Vivi, and the Warrior of Light, Mog guides them through the landscape to areas where Torsions have been opened.
Mog is also secretly working for Spiritus for unknown ends. Some of the heroes he recruits begin to suspect him of having an unknown agenda, starting when the Onion Knight observes that the things Mog says sound "rehearsed." Shantotto discovers that Mog has been hiding the true nature of "the light" from them after investigating on her own in the Domina Wastelands, and Layle, who joins under instructions from Edgar, also warns the group against taking Mog's statements at face value. Mog's choice to recruit Seymour becomes a source of friction, particularly with Yuna.
Mog becomes jittery when encountering those with telepathic abilities. He becomes concerned when Prishe says she can read minds. When he asks Krile if she can tell what he's thinking and she gives a confused "probably?" in reply (as she can speak the moogle language) he flees. He damages his credibility further in Utopia Niveus when he suggests that there's no way to be sure nobody would join Emperor Mateus, a suggestion that is rebuked by Terra's observation that Mog personally recruited every member of the party, vouching for their character each time.
Though Terra and the Warrior of Light still speak up for Mog, his decision to accept Kefka Palazzo's dimensional coordinates finally loses their trust. Although they had reluctantly accepted Seymour earlier on, and had later done the same when Kuja made overtures to ally with them, they can see nothing in the sadistic and omnicidal Kefka that would justify accepting his help.
Matters come to a head in the flower fields of the Abandoned Petalum after Vayne attaches himself to the party and eventually seizes Mog in an orb of magic. Entrapping Mog creates an out-of-control Torsion. Mog vanishes into it, and Vayne follows. After a battle with Ultima, Materia and Spiritus appear and confess that Mog deceived both of them to harness power for unknown ends. Mog's physical body vanishes from their world into the Torsion, which Spiritus dubs the "Dimensions' Labyrinth."
The entire party ventures into the Dimensions' Labyrinth wherein they meet their worst fears. As they fight through a network of barriers to reach the center, three more warriors join the group. Inside the core, the party pauses to reflect on Mog at various stages of the journey thus far; and in spite of their collective misgivings, they resolve to find him. In the distance, they find him entangled by a sinister presence known as the Blackened Will. Though weakened, Mog pleads with the party to battle the ominous creature. After they pierce its outer shell, Mog regains enough strength to reinvigorate the party and dispel some of its magic in a final confrontation with the creature's soul. With the Will's defeat, Mog is freed, and the journey continues.
Trials of the Spirit Moogle
In a special event, Terra has developed an affinity for Mog owing to her fondness for moogles in general. She alone makes a pact with Mog in spite of the party's on-again, off-again trust of the moogle. Mog reluctantly obliges and joins as an eidolon.
As a summoned spirit, Mog can enhance Terra's attributes for one turn and remove any debuffs set upon her.