Umby Pumby is the yellow Tiddlytubby. She has a Zig-Zag shaped antenna. As she is yellow, she shows quite a resemblance to Laa-Laa.
In Season 2, the Tiddlytubbies were given their own characteristics. Umby Pumby became the Sleepy Tiddlytubby. She likes yawning and falling asleep with her little teddy bear.