Snafu is a mischievous, cunning, and conniving experiment. This is proven when he turned all of Lilo and Stitch's plans to save the imprisoned experiments in Gantu's ship against them, and also sabotaged Gantu's plans to turn all the remaining experiments from good to bad. However, his desire to foil plans seems to come from his programming, and he is initially unable to distinguish friend and foe.
Snafu seems to be somewhat sadistic, as he laughs every time he manages to foil a plan. Since he was programmed to sabotage enemy plans by any means necessary, he is very resourceful, managing to outsmart both Lilo and Stitch, with even Jumba acknowledging that he can only be caught by accident. The only thing Snafu hates the most is having his own sabotage backfire on him.
Experiment 120 was the 120th genetic experiment created by Jumba with Hämsterviel's funding. He was designed to foil any and all enemy plans at whatever cost. 120 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.
At an unknown point after this, Experiment 120's pod was found by Jumba and kept in a shoebox under his bed.
Jumba warned Lilo not to use 120, as he was the worst experiment to activate when making complex rescue missions. However, at that moment, Pleakley came in with a hose and sprayed water everywhere, activating 120. He then ripped up the blueprints for Lilo and Stitch's rescue mission and escaped through the pet flap.
120 remained near the Pelekais' house, where he cleverly spied on Lilo, Stitch and the experiments' plans for the rescue mission, and sabotaged their obstacle course.
120 later foiled Gantu's plan to revert all of the rehabilitated experiments to evil by swapping the tape of Angel's song with Gantu's karaoke tape. When the tape was played, everyone on Kauai laughed in amusement.
When Lilo, Stitch and the experiments launched a rescue mission on ship, 120 tricked Sample into imitating the ship's alarm to alert Gantu. 120 then rewired the ship's prison, causing it to trap Lilo and the rescue team.
However, 120, named Snafu, did not count on the prison trapping him as well. Though after hearing Stitch confess his love for Angel, Snafu cried because it really touched his heart, causing him to turn from bad to good.
Fortunately, Snafu was freed by Angel and Stitch, who also freed Lilo and the captive experiments in their containment orbs. Snafu then foiled Gantu before the latter could recapture the experiments, and escaped the ship with Lilo, the rescue team, and the released experiments.
The first 624 experiments, including Snafu, 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 Snafu 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 ʻOe", which caused the Leroy army to shut down due to the original Leroy's fail-safe.
- Snafu is named after the acronym SNAFU (Situation Normal All Fouled Up).
- Snafu's pod color is purple.
- Snafu is described by the experiment computer screen as, "Experiment 120. Primary function: Discombobulates enemy plans."
- Despite being perfectly unharmed during the events of Leroy & Stitch, Snafu made no attempt or even showed any knowledge of Hämsterviel's plot.
- Snafu is one of the few experiments to not appear in the group photo at the end of Leroy & Stitch.
- Snafu is one of the experiments shown who isn't given a specific purpose, as in a new place to reside and use his abilities for good reasons rather than bad. It is likely, due to his expertise with mechanics, that he might be best suited for combat demolitions and undercover sabotage.