Flounder, Sebastian, and Scuttle have bad news. The Evil Witch Ursula is taking over the whole ocean! To save her friends, Ariel gives up her human form, and her prince, Eric, to rush back to the foamy depths of the sea. She must stop Ursula!
But the sea has changed. Ferocious fish prowl through coral reefs. Scary ghosts and eerie eels haunt the sunken ship. Sharks and spineballs lurk, and horrible halibut fish hide in the sand, waiting to turn Ariel into fish food.
But Ariel has tricks of her own. Her bubbles snare the finny fields and put them in a trance. Now they're harmless! Ariel can also knock out critters with magic shells, and find sunken treasures that make her faster and stronger.
But every ocean has its special guard. At the end of each maze, frightful creatures try to end Ariel's adventures. When she finally reaches Ursula's gloomy undersea lair, Ariel must destroy the huge witch whose evil powers control the sea.
--From the NES Little Mermaid instruction manual.