Jagulars are fearsome honey-stealing, predatory jaguar-like animals found in the Hundred Acre Woods. They've been mentioned several times in the Winnie-the-Pooh stories, but no real Jagular has ever been actually seen, raising doubts about their very existence.
Jagulars were first mentioned in Chapter IV of the book The House at Pooh Corner, in which Tigger and Roo are stuck on a tree, screaming for help. As Pooh and Piglet walk by, they hear the screams and Pooh believes it is a jagular. According to Pooh, Jagulars are large beasts that hide themselves in the treetops shouting "Help! Help!" But it's a trap: when people approach to help, the creature attacks. The reference to Jagular when the 4th chapter was adapted into 1974's Winnie the Pooh and Tigger Too.
Jagulars are mentioned again in the series The New Adventures of Winnie the Pooh (notably in the episode "Invasion of the Pooh Snatcher") and in the film Pooh's Grand Adventure: The Search for Christopher Robin. They're often associated with Heffalumps and Woozles, two other fearsome, frightening and possibly fictitious honey-stealing predatory animals of the woods.
In a story from the series My Friends Tigger & Pooh titled "Tigger Goes for the Jagular", Roo describes jagulars as having striped fur and a long tail. Noting the similarity, Tigger believes that he himself is a Jagular, and starts acting as such. He soon realizes, however, that Jagulars and Tiggers are totally different species.
Jagulars are also mentioned in the Winnie the Pooh film when Rabbit is attempting to get Tigger lost in the hundred acre woods. While Pooh and Piglet are walking in circles following their own tracks they hear Tigger say "Hellooooo!" in the distance. When Piglet asks Pooh what the noise was, Pooh replies that it was probably a jagular. Stating that they hide up in trees and say "Helloooo!" and when you look up to see what the noise is, they drop on you.