This post only includes adaptations in which the storyline has been changed significantly. Below is a list of different adaptations and the differences to the original story

The little mermaid 1989

• The contract: instead of dying, Ariel will belong to the sea witch once the 3 days are over
• Ariel only has 3 days to make the Prince fall in love with her
• In the original, Ariel never fought with the sea witch
• Ariel marries the prince instead of dying

The little mermaid (2018)

• the wizard gets to keep her soul if she fails to get a true loves kiss from the prince
• after she finds out the prince married someone else the wizard claims her soul
• she has to serve the wizard for all eternity
• the mermaid becomes an attraction in a circus
• she is freed by a young journalist
• when he kisses her, her soul returns to her body and she disappears into the ocean