Ariel and gang appear in various other media, and here I attempt to catalog a couple of them. (Not included are video games, theme parks and live events, which are out of my wheelhouse.)
Little Mermaid's Island
Annie Leibovitz's Disney Dreams
Once Upon a Time
Sofia the First: The Floating Palace
Descendants
Expanded universe novels
Wreck-It-Ralph 2: Ralph Breaks the Internet
The Little Mermaid Live!
Bit parts and references
Live-Action Film Adaptation
Lego Disney Princess
Disney Junior Ariel