Cannonball, despite his mischievous nature, is shown to be shy and harmless, and simply loves producing waves and often tsunamis. He also has a tendency not to look before he leaps, though he is capable of controlling the waves he creates. He is rather timid around people, but gets along quite well with others once he gets to know them. Cannonball can also be very loyal and helpful to his friends, joining Stitch's rebellion to fight off Gantu.
Experiment 520 was the 520th genetic experiment created by Jumba with Hämsterviel's funding. He was designed to turn bodies of water into huge, destructive waves and tsunamis. 520 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 520's pod landing in a bird's nest.
When a bird discovered 520's pod in its nest, it kicked the pod out, which landed in a nearby lake, activating the experiment. 520 then created a massive tsunami in the lake and began to casually make his way towards the ocean.
While 520 evaded Gantu's clutches, the former passed through the Birds of Paradise Hotel, where he then created a tsunami from one of the pools that devastated much of the hotel. In the aftermath, 520 used the pool's diving board to propel himself into the air and land safely atop a palm tree, where an incompetent Stitch catapulted him away, much to Lilo's discouragement.
520 later made his way to a reservoir while being pursued by Lilo and Stitch in Nani's dune buggy, but before he could create a tsunami, Stitch restrained him using a rope dart. However, Gantu attacked and grabbed 520, who was almost crammed into a net. Stitch fought Gantu and slipped a pineapple inside his net, leaving Gantu taking the net with the pineapple back to his ship, while 520 had been recaptured in a container.
Lilo and Stitch then released 520, and after assuring him that they meant him no harm, the three rushed off to the beach for Lilo's sand-sculpting competition. Stitch and 520 played complacently until Gantu arrived to try and capture 520 one more time, forcing Stitch to build a life-size sand fortress around himself, Lilo and 520.
When Gantu began to tear into the sand castle, 520 jumped from the castle into the ocean, where the latter created a massive tsunami that washed Gantu away to San Francisco, while leaving the island perfectly intact.
520, christened Cannonball, later found his one true place making suitable waves for surfing.
Cannonball reappeared in "Elastico" as one of the audience members for Lilo's hula dance.
Cannonball made a cameo at the end of "Swirly", where he slid into a children's wading pool.
In "Houdini", Cannonball was one of the audience members for Stitch's bungled magic act.
In "Angel", Cannonball was one of the experiments that Angel reverted to evil using her song. Later, Cannonball and the other depraved experiments attacked Stitch aboard a ship, but Angel turned them back to good before they could finish Stitch off. Working together, the experiments were then able to successfully escape the ship with Stitch.
Cannonball made another cameo in "Felix", where he was destroying the beach with his tidal waves. He was eventually stopped by Stitch, and while Lilo convinced Cannonball to tone down his waves, Stitch cleaned up the beach.
Cannonball was one of the experiments in "Checkers" that joined Stitch in a rebellion against Gantu.
In "Remmy", Cannonball was one of the experiments in Lilo's dream.
In the film's opening, Cannonball can be seen waving hello to Lilo, along with Yin and Yang. He was also seen later in the movie making perfect waves for surfing as Lilo was making her rounds with Scrump to make sure all the experiments were happy in the one true place they belonged.
Later, the first 624 experiments, including Cannonball, 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.
Cannonball participated in the following battle between the experiments and the Leroy clones by flattening attacking Leroys with his butt.
However, 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.
- Cannonball's pod color is blue.
- Cannonball is described by the experiment computer screen as, "Experiment 520. Primary function: Creates giant waves."
- Cannonball never rolled into a ball in Lilo & Stitch: The Series. However, in Leroy & Stitch, Cannonball was briefly shown to be able to roll into a ball in midair before he was captured by a Leroy clone.
- Cannonball's body appears in the online game Jumba's Lab.