The Little Mermaid AU

The Little Mermaid AU is an AU introduced through fanartt, depicting the Big Four (or at least one of the characters) as mermen and mermaids.

About the AU
This AU was formed through fanart of the Big Four (most commonly Jack and Hiccup) depicting them as merfolk or humans interacting with merfolk. Like its namesake, most writers and artists use Disney's The Little Mermaid as a template, but this is not required.

For whatever reason, this AU is most often used as a scenario for the pairing Hijack.