The corrupted entity that speaks into the ears of digimon in pain-- those dissatisfied with the state of the world, those seeking vengance, those consumed by hatred, those who feel powerless. It unravels insecurity and tugs at weakness, promising power in exchange for fealty to its own ends. Unfortunately, most digimon who accept its gifts go mad.
Allegedly, it is the corrupted form of a great evil that was sealed away aeons ago. Just over a hundred digital years ago, it began reaching out into the world. This led to God-King Dinmon severing the connection between the worlds to quarantine it and halt its growth, but it has begun to force the connection open again-- with a little bit of help from a friendly little squirrel-dragon in its employ, and a number of digimon in whom it sealed part of itself for safekeeping. As long as any part of it lingers, it can grow back.
Only Dinmon knows its true form, but it is known to the loyal by its sigil (pictured to the right).