Prepare to have your childhood ruined because these stories do not have a happy ending.
The Little Mermaid by Hans Christian Andersen. Ariel gains feet but each step she takes feels like stepping on a dagger, she dances for the Prince and becomes his favourite companion but he marries someone else who he thought saved him. Her sisters sell their hair to buy a dagger for her to kill the prince but she is unable to and ends up jumping from the ship where the wedding was and turning into sea foam.
Sleeping Beauty by Giambattista Basille. The princess splinters her finger on a poisonous flax and is then sent to one of her father’s estates. A King who happens to be crossing the estate finds her and unable to wake her, rapes her. What’s more is that she becomes pregnant and gives birth to twins while still in a coma. One of the twins sucks the splinter out of her finger and she wakes up. She then ends up marrying the King, after he burns his first wife alive because she had tried to kill the baby twins and serve them to him.
Snow White- The stepmother asks for Snow White’s lungs and liver to be served to her for dinner after Snow White dies due to the poisoned apple. The prince comes along and falls in love with her despite her being dead and starts carting off her coffin to do (???) ... things. On the way, the apple dislodges from her throat and she wakes up. As punishment for the Queen, she is made to wear a pair of red hot iron shoes and dance in then until she dies.
Mulan- Based on Hua Mulan’spoems. Mulan is kept alive by the enemy with the condition that she stay with him. Mulan is able to make an escape, but when she realises that her father is dead, she commits suicide after saying that she wants to be with her father.
Pinnichio by Carlo Collodi. Pinochhio is shown to be very bratty, rude, and impolite since the very beginning. One day, a cat and a fox, tired of his behaviour, punish him for his bad behaviour by hanging him, and watch him die.
PS: In Beauty and the Beast, Belle and the Beast turn out to be cousins.