Sneegle is a dark red, pointy-headed monster originally created for an unfinished set of safety commercials in 1962. In these PSAs for the Citizen's Advisory Committee on Highway Safety, Sneegle tempted Billy and Sue to do unsafe things, like cross the street against the light.
Sneegle was always "punished" for his carelessness -- getting hit by a car, for example. Still, he was a more appealing character than the dull Billy and Sue, and when the commercials were tested with children, the kids were more interested in emulating Sneegle's dangerous actions. The commercials were never used, and the character was dropped.
The puppet was used as a background Muppet monster in a few 1960's appearances, including the Muppets' guest-hosting week on The Mike Douglas Show.