Spats is sneaky, clever, and cunning and will do whatever it takes to start an argument. He loves to cause a ruckus and provoke a fight or quarrel. He is also a good actor and does a great job of faking being innocent and cute to get what he wants or to trick people.
Experiment 397 was the 397th genetic experiment created by Jumba with Hämsterviel's funding. He was designed to cause any pair zapped to constantly fight with each other. 397 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 397's pod landing in the window of Jumba's ship.
When the Proud Family arrives in Kauai for a vacation, Lilo, Stitch, Jumba and Pleakley invite them to stay at their makeshift hotel called "Jumba & Pleakley's Bed & Not Breakfast." Penny Proud gets more acquainted with Lilo and Stitch, while Oscar Proud complains about the hotel's accommodations. Later, Suga Mama soaks herself in a hot tub, while her dog Puff sleeps on a throw rug.
Meanwhile, a squirrel appears inside one of the windows of Jumba's ship and notices 397's experiment pod. The squirrel mistakes the pod for a nut and attempts to eat it. When it finds out it could not eat the pod, the squirrel throws it into a bowl of bath bombs. Shortly after, Suga Mama reaches for a bath bomb, but takes out 397's pod instead. Mistaking the experiment pod for a bath bomb, Suga Mama drops the pod into the bathtub, activating 397, named Spats. He then zaps the squirrel and Puff, causing the two animals to fight.
Spats later causes more mischief around town by zapping numerous pairs who end up fighting. His victims include Oscar and Trudy Proud, BeBe and CeCe, Jumba and Mr. Cooper, Lilo and Penny, Gantu and Suga Mama, and a newlywed couple. Stitch and Pleakley remain the only individuals to not be zapped by Spats' argument ray.
Meanwhile, Stitch notices Spats being pursued by Gantu. However, he manages to evade both Gantu and Stitch, and eventually hitches a ride in the back of a jeep that Pleakley is driving. Spats then teases Stitch when the latter is unable to catch up with him. After making a vain attempt to break up Penny and Lilo's conflict, Stitch chases after Spats and forcibly takes the squabbling girls with him.
Later, Stitch manages to track Spats down to an outdoor wrestling match, where the two then face off against each other on the roof of the arena. After a long battle between both experiments, Spats falls off the roof and into Penny's arms. She is angered by his presence at first, but after noticing Spats' cuteness, she starts to soften up. When Penny tries to talk to Lilo, the latter still wants to fight with her. Fortunately, Penny manages to resist her urge to fight by counting to ten and then convinces Lilo to do the same, which she does.
After Lilo and Penny make up, the former relieves the other brawling individuals by telling everyone through an overhead microphone to count to ten after Gantu, who had been wrestling with Suga Mama the whole time, went down for the count. Spats is then saved from Gantu, who has been after the experiment all this time and tried to take him away from Penny at one point.
The next day, Lilo and Stitch find Spats a one true place with Wizard Kelly. He uses Spats to make his international wrestlers fight more convincingly. Penny mentions to Lilo about having a perfect newspaper article for her school, and she, along with the rest of the Proud Family, leave on good terms.
The first 624 experiments, including Spats, 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.
Spats participated in the following battle between the experiments and the Leroy clones probably by making Leroys fight each other.
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.
- Stitch and Pleakley are the only main characters to not get zapped by Spats.
- Spats' pod color is yellow.
- Spats is described by the experiment computer sceen as, "Experiment 397. Primary function: Argument instigator."