AncientMermaidmon

AncientMermaimon is an Ancient Aquatic Beast Man Digimon whose name and design are derived from "Ancient" and "Mermaimon". It possesses the attribute of "Water", and is one of the legendary "Ten Legendary Warriors" that saved the ancient Digital World. It is the guardian goddess of the birthplace of Digimon, the "Net Ocean", ruling the whole of it and able to handle all water, such as the ocean currents and tidal waves, as if they were its own limbs. It is said that countless continents and islands have been erased when AncientMermaimon felt angry. Its abilities were later passed on to the "Aquatic Digimon".

Digimon Story: Super Xros Wars Red/Blue
If you DigiXros during a battle Mermaimon, Whamon, Scorpiomon and Coelamon, they'll form AncientMermaimon and attack with "Great Maelstrom". She can also be formed from a Digimelody.

Attacks
 * Great Maelstrom: Generates a gigantic which swallows everything in the water.
 * Crystal Billow: Crystallizes water into s, then fires them off in the manner of a machine gun.