Omaca was created durring the Eclipes, when the four Creation Ords crashed into Ultra's orb form. This resulted to a shard breaking off. The shard turned into Omaca, leaving Ultra to be unstable. Ultra and Omaca are enemies, as of the moment.
Omaca mainly seems to only use guns for his attacks (Omaca is the only Legondary Dragon who uses guns, as the others use natral moves. Omaca, though, does have one known natral move, called Dessurt Rift. First, a beam is shot from the mouth at the foe. Next, a shockwave is let loose, hitting everything in its path.
Omaca's theme is Phenomenom, by Thousand Foot Krutch