Poxy

Poxy, A.K.A. Experiment 222, is an illegal genetic experiment created by Jumba Jookiba. He is designed to enter the bodies of and infect popular planetary leaders; the symptoms are purple pimples, smelly feet, swollen eyes, and uncontrollable burping. The symptoms continue while Poxy is within the victim's body, and vanish almost immediately when he's not. He was captured by Gantu, but was rescued in "Snafu". According to a bonus feature game in Lilo & Stitch 2: Stitch Has a Glitch, his one true place is fixing health problems.

Personality
Poxy is very devious, yet carefree. He never really worries about anything and is seen multiple times messing with Lilo and Stitch. His worry-free attitude might also be a result of his great confidence. To him, everything seems more of a nuisance than an actual threat because he is unharmed while infecting somebody, not even by antibodies. So, he just makes himself right at home inside his host.

Lilo & Stitch: The Series
Experiment 222 was the 222nd genetic experiment created by Jumba with Hämsterviel's funding. He was designed to use his disease-transmitting ability to infect popular planetary leaders. The disgusting symptoms which 222's presence would cause would result in the public revolting against the infected leader. 222 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 222's pod landing in a sugar crop.

222's pod was caught up in a harvester used to extract sugar cane from the crop. The pod eventually made its way into a box of sugar, which Nani likely bought at a grocery store. A heap of sugar with 222's pod ended up in Pleakley's bowl of cereal, where the milk activated 222 before it was eaten with the cereal by Pleakley. The latter was then infected with 222's disease, and displayed the above symptoms.

Believing human doctors could help him, Pleakley headed to the nearest health clinic. While he sat in the waiting room to be admitted, Gantu showed up looking for 222. He then noticed a sick Pleakley and promptly chased the latter after realizing that he was afflicted with the experiment.

Fortunately, Lilo and Stitch followed Pleakley to the clinic and managed to rescue him by subduing Gantu with laughing gas. While Gantu was incapacitated, Lilo and Stitch rushed Pleakley out of the hospital back to their house, where they convinced him that Jumba had an ingenious method of removing 222, which would cure Pleakley.

Using Jumba's shrink ray and Nani's dune buggy to aid them, Lilo and Stitch got shrunk to microscopic size and entered Pleakley's body to find and capture 222. After a long chase through Pleakley's body, Lilo and Stitch were able to capture and extract 222 when the latter became stuck in Pleakley's earwax.

Before Lilo and Stitch finished their task and made it safely out of Pleakley's body, he was kidnapped and imprisoned by Gantu, who later took a beating from a healthy but delusional Pleakley. When Gantu attempted to crush Pleakley afterwards, the former was shrunk to microscopic size and captured. In the end, Lilo planted 222, christened Poxy, inside Gantu, who fell deathly ill from the experiment.

As Gantu was well in later episodes, it can be presumed that Poxy was extracted and sent to Hämsterviel, then later back to Gantu in "Woops" after Experiment 600 caused mischief and nearly blew Hämsterviel's cover to the prison guards.

Poxy reappeared in "Snafu", and was freed along with Gantu's other captive experiments by Lilo, Stitch, and several other experiments in a rescue mission.

Leroy & Stitch
The first 624 experiments, presumably including Poxy, 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.

It is unknown whether or not Poxy participated in the following battle between the experiments and the Leroy clones.

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 `Oe", which caused the Leroy army to shut down due to the original Leroy's fail-safe.

Trivia

 * In his episode, Poxy was microscopic size. However, in "Snafu", he was the standard size of an experiment. This might imply that Poxy can change size while functioning as a germ, but it is also possible that his container acted like a lens and magnified him to a noticeable size, as he disappeared when he was released.
 * Poxy's pod color is green.
 * Poxy is described by the experiment computer screen as, "Experiment 222. Primary function: Transmit a disease illness to planetary leaders."
 * Poxy did not appear in Leroy & Stitch, most likely due to his microscopic size.