Fleaosaurus is the name of Tweek's Flea Level. It can be found in Dinos Upstairs in Dinotopolis, on one of the toilet lids. Switch to Tweek via the Telepoint on the towel (which can be accessed with Juliette using her wall climbing ability) and enter the dinosaur's head. Tap/hit his brain and glide out of his nose, but turn around to the door on your right. You can also do this after rescuing Zweeek. They are hopping around on the first toilet lid you see.
The level takes place on Tweek's back.
- Unlike the other Fur Fighters, Tweek's level shows his scales instead of fur.