After defeating Twilight Odin in the Vile Peaks 10 AF, the party receives the Twilight Fragment Alpha, and by defeating Twilight Odin in the Vile Peaks 200 AF, the party receives the Twilight Fragment Beta.
The malevolent Twilight Odin is the 'dark shadow' that enveloped the Blitz Squadron in the Vile Peaks, 10 AF.
This entity exists outside time and can manifest in several eras at once. The source of its power, however, is but a single fragment, and the loss of this crystallized memory would weaken the shadowy being across every age.
Twilight Fragment Beta
The creature known as 'Twilight Odin' appears as a shadowy twin of the original Eidolon. In truth, it is a formless being of chaos that seeped into the mortal world from the Unseen Realm. This malignant force used a crystallized memory found in the Vile Peaks as a mold, and assumed the form of Odin.
The memory belongs to a certain l'Cie who saved Cocoon. It was in the Vile Peaks that she first faced and overcame the equine Eidolon warrior.
The player should start with an offensive paradigm, and get the chain gauge started, switch to Tri-Disaster and stagger Twilight Odin. As soon as he is staggered, the party should switch to Bully and debuff him. Buffs on the party are not essential, although they may help. The party should switch back to Cerberus and land as many attacks as possible before the chain is reset. This should take Twilight Odin to half health, after which the procedure can be repeated.
Facing Twilight Odin the second time, it is possible to debuff him from the start. It is best to start with Bully until Twilight Odin is fully debuffed. He does know Esuna and will keep healing the buffs, but it isn't necessary to continuously reapply them. The party should switch to Tri-Disaster and stagger him, switch to Cerberus and land attacks on Odin until the stagger ends or he dies. It is good to use a Feral Link (if possible) and full ATB moves just before the stagger gauge returns to normal.
Once Twilight Odin is defeated in the Vile Peaks 200 AF he will join the player party as a Commando. His development is slow at first, but his stats (particularly his HP) rapidly accelerate during the last stage of development. He is expensive to develop, requiring 269 Crystals in total to reach level 99. Once he reaches his maximum level, Twilight Odin is one of the most powerful monsters and is one of the few non-DLC monsters to achieve ATB Level 6.
A disadvantage is that he has slow animation speeds, especially when casting magic; he also requires decently wounded enemy to deal a good amount of damage due to his Bloodthirsty auto-ability. Twilight Odin's Blitz attack does good area-of-effect damage, so it is best to use him in a -W formation paradigm. His Feral Link is good at recruiting monster crystals as his Zantetsuken Feral Link gets close to 999% synchronization when performed perfectly.
None of Twilight Odin's high raw stats are augmented by stat-boosting passive abilities, so if the player infuses him with passive abilities such as HP: +35% or Strength: +35%, Twilight Odin will possess the highest stats in the game.
Twilight Odin is a one-of-a-kind monster; if the player releases him, or infuses him into another monster, the player will be unable to obtain another Twilight Odin unless they have downloaded Snow's DLC episode, in which a Level 99 Valfodr has Twilight Odin as a rare drop.