The Jiggles is a green "Gel-O" like blob made by Kowalski. Although one seriously consumed fruit, he eventually begins to rampage through the zoo, destroying objects in his path to claim his food, even 'eating' Kowalski and Julien before Kowalski was able to force the Jiggles to 'expel' them by getting Julien to remove the fish he ate for lunch from his stomach, as he couldn't regurgitate like Rico.
Although the other Penguins believe the Jiggles is dead, Kowalski has actually shrunk him down to a smaller size and hidden the Jiggles in his lab. A statue of him is displayed in the museum in Brush with Danger.
The Jiggles reappears in The Trouble With Jiggles where Skipper discovers that Kowalski kept the Jiggles alive and didn't destroy it as assigned. Kowalski explains that the Jiggles is completely harmless, having genetically modified it to no longer eat fruit, instead eating whipped cream, and no longer growing in size when eating.
It's soon discovered that instead of growing in size, the Jiggles now divides into many "Jiggli" when damaged, made worst when Skipper attempts to destroy it. The Jiggli soon escape into the zoo where they're constantly damaged and multiply out of control.
Kowalski predicts that they have just over a week before the Jiggli encompass the Earth. Having decided that Kowalski has made the situation worst Skipper instead asks Rico for options.
Rico uses whipped cream to lure all the Jiggli to one spot and blows them up, reducing their time from days to minutes. Just when everyone is about to drown in Jiggli, Kowalski incapacitates them using temperatures that only a penguin could love, then sending them into space and to the home world of the Space Squids where they pester the aliens.