Legion is a gigantic mass of corpses that forms a perfect sphere. It is a Mega Demon constructed from Nightmare's victims; further specifics are unknown. Old folklore suggests Nightmare dug a mass grave for his victims, and that, upon dumping his victims into the colossal hole, the force was so Mega that their trajectory reversed into outer space, where eventually they clumped together into a spherical mass surrounding a Mega Demon with an impressive power aura and center of gravity. Legion likes to occupy rooms full of corpses. This is surprisingly rare on G-Urth; fortunately, Legion can fashion its own room by flinging corpses at high speeds, causing the bodies to act as paint.

Explorers with a reckless disregard for their lives have tried to dig through the ball but once inside the meatmass they find themselves digging forever because it is an infinite interior of CORPSE. This has caused scientists to wonder how Nuculais ever was birthed by Legion since it would take forever to be ejected from the infinitely centered core.

Legion is a terribly lonesome creature for something that has the company of infinite people. In its spare time, it likes to eject corpses to create mini-Legions. These, having little weight in contrast, delightfully abandon the meatball upon finding it to be a terrible social partner. Although Legion wants to up its social skills, it cannot help but be rotting ball of lily-white losers.

When Nightmare was asked by an interviewer why he killed so many people, Nightmare replied, "It's just everyone who never respected me." Further research into this interview reveals that the interviewee was Hero wearing a Nightmare mask.

Legion's activities include floating and shooting lasers. Lasers are its main form of communication, and it regularly tries to impress people by pulling off radical light shows which no one attends. This is likely because Legion's venue smells like a billion corpses (the venue usually is a billion corpses).

Another legend about Legion's origin states that it is the Ultimate Orgy Machine.