The Little Mermaid

From Mental Block

The Little Mermaid is a 1989 animated musical film produced by Walt Disney Feature Animation. An extremely loose adaptation of Hans Christen Andersen's fairy tale, the film tells  the story of Ariel, daughter of Triton, king of the sea, and her romance with the human prince Eric, and the devious sea witch Ursula who manipulates her desires to gain power over the entire ocean. The success of the film kickstarted the period of Disney animation known as the "Renaissance", and its musical formula set the standard for the majority of animated films throughout the early to mid nineties.

In order to stop the budding romance between Ariel and Eric and gain control of Ariel, Ursula disguises herself as a young woman and entrances Prince Eric.