Human-sized hamster balls are, as the name indicates, hamster balls that have been made big enough to hold a human inside.
In "The Legend of the Gobblewonker," while Mabel and Dipper were eating breakfast, Dipper read a Wacky Newz periodical and showed it to Mabel. However, Mabel instantly spots an ad for the hamster ball and remarks that she was human-sized in amazement.
She then daydreamed about it, where she proudly showed it off to another hamster and then left the house, where Xyler and Craz saw her and remarked in amazement as she left. She later daydreamed about it again when they were faced with the decision of staying with their Grunkle Stan in his Stanowar or go with Soos in his S.S. Cool Dude to find the Gobblewonker. She interrupted Dipper in the middle of an interview with Charlie, where she complained that she wasn't getting an interview as well before chasing Dipper and the TV host.
The ball made another appearance in "Dreamscaperers" during Mabel, Dipper and Soos's battle against an enraged Bill Cipher in the Stan-shaped dream arena. The trio summoned one for each of them to block the dream demon's nightmare ray.
The object is pretty much what its name says: a hamster ball that is human-sized. The only variation seen in the series is colored pink.
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