The main antagonist in the movie Dragon Ball Z: Fusion Reborn.
He is a demon of pure evil and great power. Janemba is the living definition of evil to have passed through the other world and into hell. Janemba was formed due to a kid Demon's neglect to watch the evil cleansing machine. At first, Janemba was a playful, extremely large and yellow spirit like demon. After being defeated by Goku as Super Saiyan 3, he transforms into a sinister red demon.

Upon sensing the power of Janemba in his first form, Goku says that it is the strongest power he has ever felt (he may have been referring to Janemba's reality manipulation abilities along with his raw strength).

he then proceeds to compress himself into a smaller space, resulting in this new form. This form is able to use a deconstruction/reconstruction teleportation known as the Bunkai Teleport, portals with which he can attack through, stretch his arm at lengths, turning objects into deadly weapons, project his opponents' own Ki Blasts back at them through portals.

He wields a powerful sword capable of shooting unblockable ki strikes, though Vegeta, who arrived to help Goku, destroyed this sword.

In his super form neither Goku or Vegeta were able to beat him.