When Billy, Mandy and Grim attend an Ancient Egypt exhibit at the museum, they meet with Irwin who explains that, as his mother is a mummy, they are visiting Irwin's grandfather, the great Pharaoh King Popen Locken. Later that night, Irwin's grandfather visits Irwin in his room and offers him the Pharaoh's crown and the possibility of building his own pyramid to attract women; Irwin accepts, calling himself King Tooten Pooten, and soon they turn the citizens into slaves to build the pyramid. Against his mother's wishes, Irwin decides to finish the pyramid; however, there is something he did not anticipate, as he, the Pharaoh, needs to remain entombed inside it.

A scene of Endsville two weeks into the future shows a dystopian world ruled by the "Lord of Horror", who wields the all-powerful artifact known as "Horror's Hand". At the same time, two robotic replicas of Billy and Mandy are sent into the past, to stop the real Billy and Mandy from interfering with the current events.orror's Hand to rule the world.