Stuffed creature of indeterminate species

 is a prize in the ball toss game in the Mystery Fair.

History
Wendy asks Dipper to win her one of the creatures of indeterminable species when the ball bounced and accidentally hit Wendy in the eye and gave her a black eye. Robbie then comes up and takes his snow cone and uses it as an ice pack on Wendy's eye when he asked her to be his girlfriend.