"There's no need to fear, Underdog is here!" Transform your pooch into the beloved cartoon Underdog in this Underdog Dog Costume! Your best friend is sure to save Sweet Polly Purebred (or pretty much any neighborhood dog) against those neighborhood Bullie-dogs this Halloween. But be sure to keep him on a leash, or he might just try to fly up up an away! You know how it goes, you give your dog a cape and it goes straight to his head.