Drives Like Crazy: When Eric shows her around his kingdom, he lets her have the reigns to the carriage. She apparently only knows enough to make the horses go even faster.
Foot Focus: The scene right after the transformation sequence seems to be dedicated to this, as she starts getting used to her new appendages. She's the source of the current trope image, in fact.
Hoist by Her Own Petard: She decides that it's best for Melody's safety to keep Melody ignorant of her true origins and heritage. But Melody's ignorance (and Ariel's unwillingness to be truthful when she finds the locket) is exactly what causes her to run away and go against her mother until Morgana reveals her true colors.
Former Teen Rebel: In the sequel, she scolds Melody for doing basically what she used to do as a teen. Granted, she did have good reason, but all she ever told Melody was to stay out of the ocean.
Adaptational Villainy: In the fairy tale, the sea witch was a neutral character who in addition to warning the mermaid of the transformation's consequences, didn't go back on her deal with the mermaid until asked to, and never interferes directly.
Ink Suit Actor: Subversion; Ursula was actually based on the drag queen Divine, who was originally supposed to voice her, but died before he could even record the voice, so the role went to Pat Carroll instead.
Kick the Dog: A literal example in her human form.
