Edio Yenye Shavu

When SpongeBob found Mermaid Man's belt and accidentally shrunk Squidward, he started shrinking anyone who found at until he could figure out how to regrow them. Once he admitted the mistake to Mermaid Man, Mermaid Man revealed there wasn't a grow option and the solution was to shrink down all of Bikini Bottom so they would all be the same size again. This would explain why Mermaid Man and Barnacle Boy are the size of fish even though they're human