The Immortal Avatar True Doomsday Body granted unbelievable survival skills. Unless you could annihilate his soul with a single thought, trying to kill a Neo-Demon with this type of body was almost impossible.
The Immortal Avatar True Doomsday Body allowed the user to divide his actual body into avatars that could act utterly independently from each other. Each of those avatars could go to wars, train, and experience everything the original body could.
While Neo-Demons can form multiple avatars, they only had one True Soul, True Doomsday Body, and True Will that would remain in one of the avatars' soul dimensions.
But this is where the amazingness of the Immortal Avatar True Doomsday Body presented itself. The True Soul, True Will, and True Doomsday Body could instantly teleport from one avatar to another.