The Little Mermaid and the Sea Witch
Sea witches have been featured in European folklore for centuries. The most well-known one is the Sea Witch from "The Little Mermaid" by Hans Christian Andersen.
In fairy tales[]
The Little Mermaid[]
When the Little Mermaid first meets the Sea Witch, she is described as a disgusting old hag who allowed a toad to eat from her mouth and had two water-snakes as pets whom she called "chickens". As payment for transforming the Little Mermaid into a human, the Sea Witch wants her voice as it is "the sweetest voice of any who dwell here in the depths of the sea". When the Little Mermaid agrees, the Sea Witch cuts out her tongue and brews a potion that includes several drops of her own black blood, alongside several other disgusting ingredients.
The Sea Witch isn't seen again after this, but is mentioned at the end of the fairy tale. As the Little Mermaid awaits the sunrise so that she may die of a broken heart (as the prince has married another human princess, the catch to her deal with the Sea Witch) she is visited by her five older mermaid sisters who have traded their hair to the Sea Witch for a magical dagger. With this dagger, the Little Mermaid must stab the prince in his heart and let the warm blood fall on her feet so they may transform back into a fish-tail and she can return to her life as a mermaid under the sea.
Mythology[]
A sea witch named Morgana was a main contributor in luring sailors to their deaths. After falling in love with a young hero who was sadly lost to the sea, she vowed to help other heroes and sailors in their travels. This caused her to be outcast among her sisters. After trying to help a son of Ares she was impaled with a spear and dissolved into the sea foam, her final resting place.