His first appearance was in Under Wraps. He was sent by Viktor to find a dangerous element called Corrodium that had crashed on Earth millions of years ago. Todd Maplewood, a boy Ben and Gwen met, said it arrived in a flash of purple lightning, which is the same way the Yenaldooshi arrived in Benwolf.
Grandpa Max states there may be a connection between the Yenaldooshi and Mummy, which is proven in The Return. During Ben's battle with the creature, its DNA is scanned by the Omnitrix, giving Ben access to the form. The Mummy is frozen solid by Upgrade merging with a liquid nitrogen device and buried, along with its Corrodium, under a thick bed of concrete.
It was later released by the werewolf in The Return, and assists in Dr. Viktor's plan to plunge the earth into eternal darkness. When Ben is fighting Zs'Skayr, Doctor Viktor, and The Mummy in Be Afraid of the Dark, Doctor Viktor inadvertently sends both himself and The Mummy to the Null Void, through an ill-timed use of his teleportation device.
Powers and Abilities
The Mummy can extend his bandages to great lengths and wrap his enemies in them. He can also crush people with them against an object. He can also unwrap himself, causing projectiles thrown at him to go through him. His physiology allows him to carry things within him. In this manner, he can carry Corrodium without any of the radiation being released, He is also able to survive in the vacuum of space.