The Pumpkinator is an evil villain that destroys planets by growing vines which dig into the surface of the planet. It then causes a countdown to explode. When the countdown reaches zero, the Pumpkinator explodes, the planet going along with it. In the television special that Timmy was watching, the Pumkinator splits back into the original Jack-O-Bot forms after it destroys the pumpkin-shaped planet Crash Nebula tried to save.
At 30 feet tall, the Pumpkinator is shaped like a jack-o'-lantern with two arms and two legs. It also wears a horned helmet on its head, and has vine appendages which dig into the surface of the planet while it is counting down to explode. A countdown timer appears out of its helmet when it is about to destroy itself and the planet it is on (it is somewhat immune to the explosion since in the TV special Timmy was watching, its separate Jack-O-Bot components were able to survive and go off in search for another planet to destroy). It is equipped with rocket lauchers in its shoulders and a powerful flamethrower in its mouth.
The Pumpinator created by Timmy's wish spoke with the voices of the popular kids. However, when the coundown timer reached one minute, it briefly spoke in a deeper, more demonic voice. During its second appearance on Unwish Island, it spoke with this voice all the time.
When Timmy wished that everyone's Halloween costumes would become real and scary, everyone become real and scary versions of the costumes they were wearing. The popular kids (Tad, Chad, Trixie and Veronica) had been wearing authentic Jack-O-Bot costumes, and were turned into actual Jack-O-Bots. When all four of the Jack-O-Bots merged, the Pumpkinator was created. It planned to transform into a giant doomsday device that would destroy the Earth. After four minutes, it transformed and started counting down from 59 seconds (with the popular kids audibly counting down impatiently). Just before the timer ran out, Timmy unwished the wish he had made and the Pumpkinator was turned back into the popular kids in costumes, who fell together into a harmless pile.
The Pumpkinator reappeared in "Escape From Unwish Island". Since it was wished away, it became a resident of Unwish Island where it, and like everyone else on the island, has a deep hatred for Timmy. Thanks to Timmy's efforts, he was able to make peace with the Pumpkinator along with all of the other residents of Unwish Island by creating Timmy clones that the residents can torment and a five star resort hotel for them to reside in as well as an 'I Hate Timmy" club where the residents are all members.