Swapper, A.K.A. Experiment 355, is an illegal genetic experiment created by Jumba Jookiba. He is designed to switch people's minds; it is possible for him to swap more than two individuals at once. According to Jumba, 355 once swapped the former and his wife for an entire month, which led to a divorce in the end. His one true place is in the hospital doing brain surgery. He is voiced by Frank Welker.
In his episode, he switches Lilo with Stitch, Jumba with Pleakley, Hämsterviel with Gantu, and eventually switches all four protagonists' minds back into their original bodies. In Leroy & Stitch, he is seen playing the bongos.
Because Swapper is two heads on the same body, Swapper is two beings cooperating as one, though their personalities mirror each other: they can be indecisive at times but usually work well together. An example is when Stitch in Lilo's body asked the two-headed cousin to switch their minds back, Swapper, after hesitating, blew a raspberry in response. The two enjoy messing with people by swapping their brains and refuse to switch them back unless threatened. However, Swapper will switch individuals' minds back into their original bodies when both heads choose to do so.
Swapper is a two-headed, four-armed green lizard-like experiment with no tail, black eyes, stubby legs, purple markings on his back and three purple-tipped tendrils on each head.
Swapper can emit a green ray from each head's eyes once each head is pointed at one of two individuals, but one time he hit four beings at once, although the complete limit of beams is unknown. The ray will swap the minds and voices of the targets, as well as vice versa, and the only means of returning to normal is through Swapper choosing to do so. Swapper has some of the basic experiment attributes, including scaling walls and rolling into a wheel-like shape, rather than the basic ball-like.
Swapper has shown to be skilled in playing the piano/keyboard.
Swapper is terrified of Pleakley's disgusting cuisine, as he immediately gave in to obeying once threatened with only being fed with it.
Swapper made an appearance in the Stitch! anime where he used his powers on Stitch and Hiroman. Until they could find Swapper again, Hiroman needed to figure out how to use Stitch's abilities to take on Heat. After Heat, Gantu and Reuben were defeated, Jumba made a request for Swapper to swap Stitch and Hiroman back into their original bodies, but he instead swapped everyone's bodies again!