Phantasmo is a mischievous and ghostly experiment whose intangibility allows him to possess inanimate objects and wreak havoc through them. He also has a tendency to gloat by laughing in a squeaky voice. He would act inanimate because if anyone exposed him or knew his secret, he would then become feared or hated, so he would dispose of those who found out. However, he later decided that receiving adoration from people was better than causing chaos.
Experiment 375 was the 375th genetic experiment created by Jumba with Hämsterviel's funding. He was designed to possess inanimate objects and, through them, cause massive mischief and chaos. 375 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.
375's pod eventually made its way into a prized oyster inside the Macki Macaw restaurant's crane game.
Stitch played the claw game and won the oyster, but a glitch in the machine caused him to shake it in frustration, which led to him having a conflict with Nani and one of the employees. After the oyster freed itself, Lilo and Stitch took it home with them.
When Lilo tried to give Stitch a bath, the latter lay hidden in the laundry hamper, but she tricked Stitch into coming out and dragged him to the bathroom. There, an incident with the bathtub (having overflowed after Lilo dunked Stitch in the tub) resulted in the oyster opening and the pod inside getting wet, activating 375.
That night, 375 wreaked havoc in the kitchen. When Stitch was alerted, he attempted to save Pleakley's dishes, but 375 made Stitch lose his balance and shatter them. 375 then possessed Scrump and used the doll to paint Nani's face green, sabotage Jumba's experiment analyzer, steal Pleakley's begonia, break Lilo's record player, brush Nani's toothbrush on Stitch's toes, and frame Stitch for it all.
The next morning, Nani, thinking Stitch was the culprit, threw him outside and forced Lilo to chain him up as punishment. However, Stitch soon noticed 375, who was using Scrump again to unravel Lilo's Elvis videotapes. Stitch broke free and attacked Lilo's doll, arousing her suspicion. When Stitch was later being prosecuted, he saw 375 (still inside Scrump) wink at him, causing Stitch to lash out at Lilo's doll.
Later that day, while 375 was attempting to break Pleakley's flower pot to get Stitch in deeper trouble, Lilo caught him right in the act. 375 revealed himself and possessed a rope, with which it tied Lilo, Jumba and Pleakley up. He then repossessed Scrump and prepared to execute the three with Jumba's blaster, but a vigilant Stitch ambushed 375 and freed his ʻohana.
While the four searched for 375, he possessed a vacuum cleaner and almost sucked Pleakley up with it. Lilo and Stitch then made a vain attempt to catch the intangible 375, forcing the latter to retreat into Kokaua Town.
After a long pursuit through town, Nani rescued Lilo and Stitch in her jeep and led 375 to the Macki Macaw restaurant, where he used the claw machine to trap Stitch. The former then chased Lilo backstage and possessed the Macki Macaw animatronic that had malfunctioned sometime earlier. Eventually, 375 put on a show for an audience after Lilo raised the curtain.
375, christened Phantasmo, was then convinced by Lilo that using the animatronic parrot to entertain children and receive adoration was a better way of gaining attention than causing chaos, thus giving him a one true place.
Phantasmo made a cameo inside the Macki Macaw animatronic on TV at the end of "Snooty".
The first 624 experiments, including Phantasmo, 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.
Phantasmo 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.
- Phantasmo was first revealed in a DVD bonus feature of Stitch! The Movie in the experiment gallery.
- Phantasmo is clearly a spectral being, as he possesses intangibility and the ability to phase through obstacles, thus making him the only experiment that cannot be restrained or captured.
- This would come into question in Leroy & Stitch on how he was captured by a Leroy clone. Also, he was seen being chased by another Leroy clone with a plasma gun, despite his inability to sustain physical injuries.
- Phantasmo's pod color is yellow.
- Phantasmo is described by the experiment computer screen as, "Experiment 375. Primary function: Spiritual possession."
- Phantasmo's ears appear in the online game Jumba's Lab.
- Phantasmo is similar to the five Possessors in the game Luigi's Mansion: Dark Moon, as they are able to possess inanimate objects and attack through them. The only difference is that one Possessor was able to possess a living being (a spider queen).