In a flashback scene of Lilo & Stitch 2: Stitch Has a Glitch, Jumba was in his laboratory, where he had just finished creating Stitch and attempted to fully charge Stitch's molecules in order to prevent him from short-circuiting and dying. However, a prison guard suddenly burst into the lab and apprehended Jumba for illegal experiment creating, thereby disrupting the process.
In Leroy & Stitch, after Lilo and Stitch had successfully turned all of Jumba's experiments from bad to good, he was given the confiscated key to his laboratory again. Jumba was at first happy to be returning to many of his "evil genius" ways, but discovered that without anyone to show his accomplishments to, he was as unhappy as Pleakley and his job at G.A.C.C..
However, Jumba's sadness was short-lived when Gantu and Hämsterviel barged in. Hämsterviel then forced Jumba to create a new and better experiment to defeat the Galactic Alliance. After Jumba finished creating the experiment and activated it, Hämsterviel named him Leroy. Later, when Stitch burst in to recapture Hämsterviel, the latter ordered Leroy to kill Stitch, and a fight ensued between the two experiments. During their prolonged battle, they unintentionally sabotaged Jumba's lab, much to his horror because he had no insurance.
While the lab was left in shambles, Stitch eventually had Leroy pinned down, but Pleakley's untimely arrival distracted Stitch long enough for Leroy to bat him into a containment orb. After Leroy proved to be more powerful than Stitch (although he technically didn't win fairly), Hämsterviel cloned Leroy into a huge army and sent the captive Stitch, Jumba and Pleakley off to a black hole (though they managed to get out safely).