Serena is a small mermaid who only appears in the episode The Littlest Mermaid. A strong gust of wind sends her trapped in a huge wad of seaweed not far from the Snorkland city limits. Allstar, Dimmy, and Casey save her as well. Dimmy immediately falls for her, and she spends the night with Casey. Serena is a small mermaid, and her sisters are bigger than her, so she obviously has some insecurities about her size. Dr. Strangesnork learns about her, so he plans on increasing his size so he could control her. This leads to chaos, and she is zapped by the lazer causing her to be just as big as her sisters. But they have already accepted her no matter how big or small she is. In the end, Serena goes home to be with her sisters.