TwistedTale is an au where the characters are sick, twisted versions of themselves.
Frisk fell from Mt. Ebott onto Golden Flowers. Despite the gender being unknown in Undertale, Frisk is a female in this au. After a long journey, she falls in love with Monster Kid.
Flowey, instead of being yellow, is blood red, and has fangs. He throws bullets, which must be avoided or you'll die. He gains a crush on Frisk in the end.
She is still a motherly character, but does no care about your safety. However, she fights you so you don't meet Sans. She and Sans get together in the end.
Still a lazybones, however, if Frisk is about to die, he pokes in and saves her. He and Papyrus are the only two with a sense of morality. He and Toriel get together in the end.
Still his goofy, overconfident self, however, he is hiding dark secrets about his "training" with Undyne.
He is a tiny bit older in this. He is unaware of Undyne's abusing Papyrus and views her as a hero until he discovers the secrets.
She is Papyrus's trainer, but instead of training him, she beats him up, showing no mercy towards him. She often makes fun of him for not fighting back. She and Alphys are lovers.
She formerly built Mettaton to entertain, but put mind-control software into him, mind-controlling whoever was watching the show. She attempts to kill Frisk. She and Undyne are lovers.
When Alphys installed the mind-control, he attempted to run away but did not get far due to Undyne. He has a crush on Muffet.
She doesn't change much. She gains affection for Mettaton at the end.
When seen in the ruins, he uses TRAP MODE so you cannot get away. He is more ruthless than his Undertale counterpart. He has a deep hatred for Sans, as he bought something faulty from Sans.
He is even worse than Undyne, as he does not allow you to run away since the beginning. The one thing that can stall him is a call from Papyrus, allowing you to run.