Experiment 151 was the 151st genetic experiment created by Jumba with Hämsterviel's funding. He was designed to turn entire civilizations into babies, throwing the planet into unsupervised chaos. 151 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 151's pod landing on a sidewalk.
When the Ice Cream Man tripped on 151's pod, it rolled across a nearby beach shore and into an ocean wave, activating the experiment. 151 then proceeded to turn the tourist into a baby, causing him to behave like an actual infant. He was later spotted by Lilo and Stitch, who consulted Jumba and learned about 151's powers.
Later, 151 went on a rampage, turning others, including a construction worker, into babies before Stitch was able to capture him in a bucket. After having a brief feud with Nani, who mistook Lilo and Stitch for trying to sneak off to the movies unsupervised, they took 151, named Babyfier, back to their house.
That night, Stitch released Babyfier on Nani so Lilo could be in charge for once. However, after turning Nani into a baby, Babyfier turned Stitch, Jumba and Pleakley into babies too. Babyfier then attempted to do the same to Lilo, but the former was lured into a trap and recaptured, leaving Lilo to look after her de-aged ʻohana.
When Experiment 625 discovered that Babyfier turns adults into babies, he released Babyfier on Gantu. However, after turning Gantu into a baby, Babyfier attempted to do the same to Reuben, causing the latter to lock Babyfier out of the ship. Hämsterviel was then alerted and demanded them both to retrieve Babyfier.
Meanwhile, the babyfied Jumba (who still retained the personality and intellect of adult Jumba) managed to find a cure on his computer that would reverse Babyfier's effects. Lilo despaired when she saw that one of the ingredients for the antidote was a dollop of 100% Kona coffee, which only adults were allowed to buy.
Outside with her infantile ʻohana, Lilo tried coaxing a passing couple to buy her the desired coffee before Babyfier turned them into babies. A moment later, Reuben and the babyfied Gantu pursued Babyfier as he went on a second rampage, followed by Lilo and the babyfied Nani and Stitch.
Meanwhile, the babyfied Jumba and Pleakley traveled to Kiki's Coffee Hut, where they found several bags of 100% Kona coffee on a shelf to make the remedy for undoing Babyfier's effects.
Later, the babyfied Stitch and Gantu tracked Babyfier down to a playground, where the two fought over him while bickering, with Stitch winning. After Babyfier was recaptured, Jumba and Pleakley (back to their normal age) arrived with the antidote. Stitch blasted it into the sky, turning all the babies on Kauai except Gantu back into adults.
Babyfier was then found a one true place at the dog shelter, where he turned old dogs into adorable and more adoptable puppies, effectively giving them a second chance at finding a new home.
It can be presumed that the babyfied Gantu was somehow turned back into his adult self, while Reuben was forced to babysit Gantu in the meantime.
In "Ploot", Babyfier was one of the second team of experiments (along with Finder and Drowsy) formed to try and stop Ploot. However, Ploot was easily able to defeat them, forcing the three experiments to retreat.
Later, the first 624 experiments, including Babyfier, 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.
Babyfier participated in the following battle between the experiments and the Leroy clones by turning Leroys into babies.
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.
Babyfier made an appearance in Season 2 of the Stitch! anime along with Hammerface, Link, Spike, 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, Babyfier was reprogrammed by Hämsterviel to transform his victims into toddlers instead of babies (and appropriately renamed Toddler-fier). He left Stitch in charge of several schoolchildren whom he turned into toddlers, including Yuna herself.
- Even though Stitch was not born as a baby (being a genetic experiment), Babyfier still managed to turn him into an infant.
- Babyfier's pod color is white.
- Babyfier is described by the experiment computer screen as, "Experiment 151. Primary function: Infant maker. Change the victim into their infant form."
- Babyfier's tail appears in the online game Jumba's Lab.
- Babyfier bears some resemblance to Mew from Pokémon, even having the same designation number, 151.
- In the English dub of the Stitch! anime episode "Link-age", Reuben states that Babyfier's favorite type of sandwich is puréed carrots.