Role in the series
Because of Dr. Vile's electric waterwheel which is used to give him electric power in order to perform his own crab experiments around his castle on an island, the ocean has been polluted by a stream of green liquid, thus, causing the fish to fall terribly ill. So, Ariel, Flounder, Sebastian, and Scuttle decide to investigate and put an end to this.
While Ariel and her friends go inside to find the source of the pollution within the castle, Sebastian cowardly stays out as a lookout only to get captured by Dr. Vile so as to use him as another test subject for his crab experiments. Dr. Vile intends to get his creation right this time with Sebastian unlike with the previous ones before him including his monstrous crab mutant assistant, Igor. The moment Dr. Vile boasts about making Sebastian bigger, fatter, and tastier, Sebastian panics and escapes with his life. Despite Dr. Vile and his other crab mutant monsters' best efforts to stop him, Sebastian manages to escape momentarily. Later, Dr. Vile tries to trap some sea food to feed his crab monsters, namely, Ariel and Flounder.
Dr. Vile finally manages to locate Sebastian in the room of his young but kind apprentice, Daniel. As punishment for denying to give him Sebastian, Dr. Vile offers Daniel a few days of bread and water to improve his attitude. Then, Dr. Vile tries to perform his experiments on Sebastian again, only this time, he has him stripped to the table to avoid any escape. Luckily, Scuttle arrives just in time to rescue Sebastian before the green liquid, which is used to mutate crabs and one of the sources of the ocean pollution, comes in contact with Sebastian; much to Dr. Vile's chagrin.
Later, Dr. Vile captures Daniel and threatens to turn him into a human crab unless he reveals the whereabouts of Sebastian to him, which he obviously remains oblivious to as well. Luckily, Ariel manages to destroy the waterwheel using a monkey wrench, an idea originally thought out by Daniel when he was befriending Sebastian, thus, causing the machine and part of the castle to explode and cease the pollution in the ocean.
After Ariel's father, King Triton creates thunderstorms to destroy the remaining green liquid left in the ocean, back at the castle, Dr. Vile naively blames Sebastian for this mess and vows to get his revenge on him if it's the last thing he ever does.
- Dr. Vile was voiced by the late Kenneth Mars who also voiced King Triton in The Little Mermaid franchise.
- Dr. Vile's assistant is named Igor; a reference to Dr. Frankenstein's own assistant, Igor.