Experiment 455 was the 455th genetic experiment created by Jumba with Hämsterviel's funding. She was designed to be the bouncer for Jumba's lab and hip-check unwanted guests. 455 and the other first 624 experiments were deactivated and smuggled to Earth by Jumba during his mission to capture Experiment 626.
All of the experiment pods were released and scattered across the island of Kauai, with 455's pod landing in a sugar bowl by a coffee shack.
Later, a woman mistook 455's pod for a sugar cube and dropped it into her coffee, activating the experiment.
At an unknown point after this, Experiment 455 was presumably captured and named Mary. She seemed to have a craving for exercise, and displayed it after she bounced Stitch into a palm tree. It is unknown what episode this was shown in.
Mary was one of the experiments that was gliding on the screen, but she is 536 instead of 455.
The first 624 experiments, including Mary, were rounded up by Leroy and taken to a stadium to be destroyed. However, Lilo, Stitch, Jumba, Pleakley, Reuben and Gantu arrived before the experiments could be destroyed.
Mary participated in the following battle between the experiments and the Leroy clones, but it is unknown what she did.
The Leroys soon gained the upper hand in the battle, but were defeated when Lilo, Stitch, Reuben and several other experiments performed the song "Aloha ʻOe", which caused the Leroy army to shut down due to the original Leroy's fail-safe. Mary can be seen in the audience bouncing. This proves that she rather bounces than walks.
- Before her name was revealed, most people thought 455 was male. But 455 is actually female.
- 455's original name was going to be "Hippy" because she hip checks people.
- Jumba briefly considered giving Mary the number "086" as a little joke on Quelte Quan, as here, to "86" someone means to remove them from the premises, but the number was already taken by Clink.
- Mary seems to always be smiling, but she can be quite vicious as seen in Leroy & Stitch.
- Mary's pod color is red.
- Mary is described by the experiment computer screen as, "Experiment 455. Primary function: Hip checking unwanted guests."
- Mary is one of the few experiments to not appear in the group photo at the end of Leroy & Stitch.