|Type||Ancient Aquatic Beast Man|
|Cards||(Ja:) St-914, Bo-843, Bo-1044|
AncientMermaimon is an Ancient Aquatic Beast Man Digimon whose name and design are derived from "Ancient" and "Mermaimon". Possessing the attribute of "Water", it is one of the Ten Legendary Warriors that saved the ancient Digital World. A Mega who existed only in the distant past, 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".
D-Tector 2.0 and 3.0
Digimon Story: Super Xros Wars Red and Blue
AncientMermaimon is a Mega-level Digimon. It can be digifused during battle from Mermaimon, Whamon, Scorpiomon, and Coelamon, and will attack with "Great Maelstrom". It can also be formed from a DigiMelody.
- Great Maelstrom: Generates a gigantic maelstrom which swallows everything in the water.
- Crystal Billow: Crystallizes water into supersolids, then fires them off like a machine gun.