Cthyllamon resides in the depths of the Net Sea. In the pitch black waters, only the skull on its chest is visible, appearing to float eerily through the darkness. This has earned Cthyllamon the alternative title, "phantom of the sea."
This Digimon has a crafty disposition, and does not join fights of its own volition, instead brainwashing weaker aquatic Digimon and using them to fight on its behalf. Cthyllamon is seen very rarely and resembles MarineAngemon in many ways, but it is unknown whether there is any connection between the two.
In its Ocean Hell technique, Cthyllamon uses an aura of endless terror as unknowable as the dark depths of the ocean to sap its enemies of their will to fight. Digimon that suffer this attack are sometimes reduced to Cthyllamon's puppets. For its Buccal Rush technique, it opens its mouth wide and attacks using its three whip-like tongues. Lastly, with its Aqua Grinder technique, Cthyllamon can create fierce whirlpools that bore into enemies' bodies like a drill, displaying a destructive power that one would never imagine such a tiny creature capable of.