Fusion

[Fusions are listed as "uncanon" in official lore, and are used for 'Bahamut Legends.']

Fusion involves the blending of 2+ distinct entities into a single being. While fusing, separate attributes of these entities are combined, including wisdom, reflexes, strength, intelligence, and speed. When the entities are fused properly, the fusion that's made acquires an extraordinary power level that is much beyond the bounds of what the original entities had initially. Currently, there are a variety of fusion methods as well as many kinds of fusions.