Spike is shown to be very troublesome, as his spines pose a dangerous threat to anyone pricked by them. He also has a feisty side to him and will attack any target, even if he's outnumbered. However, he is not afraid to show emotion as seen when he cried noisy tears while Pleakley hugged him during the E.A.R.W.A.X. session. This not only rehabilitated Spike, but also motivated him to be a hugging therapist and follow Pleakley's hugging-and-crying method.
Experiment 319 was the 319th genetic experiment created by Jumba with Hämsterviel's funding. He was designed to fire spines like darts that make his victims unintelligent by causing any hit victim's goofiness level to increase by 99%, leaving them only 1% clever. 319 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 319's pod landing by an outdoor stage.
When a clumsy servant carrying drinking water bumped into the public speaker, the water bottle on the tray fell onto the stage and trickled out, which touched 319's pod, activating the experiment. 319 then spiked Dr. Okra and her servant, causing them to act goofy, and then attacked the entire audience.
Later, 319 attacked a museum until he was captured in a containment orb by Stitch, but not before spiking him and Jumba. Luckily, 319's goofiness-inducing spines didn't seem to affect Jumba as much as Stitch (since the former was already a genius).
While the captive Spike was being rehabilitated, Lilo made a vain attempt to get a goofy Stitch to become smart again in time for the upcoming Ohana-Rama contest.
During Pleakley's seminar, he bored most of the experiments with Dr. Okra's therapy topics. When a fight broke out between Slushy and Splodyhead, a stray fireball from Splodyhead destroyed Spike's container, freeing him. Spike then went on a rampage, chasing Nosy around the house and eventually targeting Pleakley.
Forced to resolve the matter, Pleakley left for a moment and donned knight's armor against Spike's spines. He then attempted hugging therapy on a feisty Spike, which surprisingly pacified the latter, who sobbed pitifully. The other experiments, awed by Spike's outcome, tried out Pleakley's hugging-and-crying method as well.
The following night, Lilo, Stitch, Jumba, Pleakley and Spike attended the Ohana-Rama, where Mertle sunk Lilo's team by answering each question correctly. Spike then offered Lilo a hug to cheer her up when she felt discouraged. She declined, however, because although Spike was rehabilitated, a stray spine would likely affect her intelligence.
Later during the contest, Lilo and Spike followed Stitch backstage to discover Teresa was secretly helping Mertle cheat. Thus, Lilo convinced Spike to hug Teresa, who got pricked and kept giving Mertle completely silly answers as a result. After Lilo won the Ohana-Rama, Mertle stormed out in a rage. Spike felt sorry for Mertle and decided to hug her as well, spiking the latter.
Spike was later found a one true place in Pleakley's E.A.R.W.A.X. group, using hugging therapy to tame other truant experiments, while wearing similar knight's armor to cover his goofiness-inducing spines.
The first 624 experiments, including Spike, 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.
Spike participated in the following battle between the experiments and the Leroy clones by firing goofiness-inducing spines at Leroys.
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.
Spike made an appearance in Season 2 of the Stitch! anime along with Hammerface, Babyfier, Link, and Woody. It is revealed that Hämsterviel reverted these experiments to evil using a recording of Angel's song, thus enabling them to wreak havoc on the island. In another episode, Spike was also used by Hämsterviel to try to sabotage a quiz competition. His abilities were modified in this episode so that he only reduces the victim's intelligence, and it can be magnified by squeezing his nose. It is shown that he has the ability to roll into a ball and launch his spikes while spinning at incredibly high speeds.
- Dr. Gladys Okra, Spike's first victim, bears a striking resemblance to Oprah Winfrey.
- When Jumba got pricked by Spike, he did not act stupid since he was already a genius even by 1%, indicating that he is the only one immune to Spike's goofiness effects, though he still felt the pain from the spines alone.
- Spike is clearly a porcupine-like experiment, but unlike him, real-life porcupines cannot throw/shoot their quills, nor are their spines poisonous.
- Spike is one of the six known experiments to be rehabilitated by someone other than Lilo and Stitch, the other five being Gigi, Elastico, Yaarp, Frenchfry, and Snooty.
- Spike's pod color is yellow.
- Spike is described by the experiment computer screen as, "Experiment 319. Primary function: Makes victims act goofy and stupid."
- In the English dub of the Stitch! anime episode "Link-age", Reuben states that Spike's favorite type of sandwich is shish kebab euro.