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. When the countdown reaches zero, the Pumpkinator explodes, the planet going along with it. In the television special that Timmy was watching, the Pumkinator split back into the original Jack-O-Bots after it destroyed the pumpkin-shaped planet it was on.
30 ft tall, the Pumpkinator is similar in shape to the Jack-O-Bots: it is shaped like a jack-o'-lantern with arms and legs. It also wears a horned helmet on it's 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 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 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 together, 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. Just before the timer ran out, Timmy unwished the wish and the Pumpkinator was turned back into the popular kids in costumes, who fell together into a harmless pile. Since it was wished away, it became a resident of Unwish Island where it, like everyone else on the island, has a deep hatred for Timmy.