The Little Mermaid (1992)

Season 1: Episode 10

Prince Eric drops one of his boots down to the sea, and when Ariel finds it she thinks its a wonderful human thingamajigger, but Triton thinks its dangerous. Soon terrible things start to happen and every sea creature thinks that the thingamajigger is the cause, so every bad guy wants it to take over Triton's kingdom, but Ariel goes to the surface and finds out what they really do.