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The Coney Island Kelp was the disguise of a member of a team that entered the float "Oceanic Splendor" in the Coney Island Mermaid Parade
Scooby-Doo! (DC Comics)
They were afraid of the humiliation of not coming in first after winning year after year. One of their members dressed as the Coney Island Kelp to steal the trophy and ruin the contest. The other helped by lying for him and trying to put the blame on Ellie May Pike.