Toriel is the caretaker of Ruins, and the second monster Aliza met.
Toriel has overall darker colors, and her dress is more torn. She also has more visible eyelashes and bags under her eyes. Unlike the original Toriel (who has dark red eyes), Horrortale Toriel's eyes are light green.
She still keeps her motherly characteristic. But she is less sane, and more willing to do much violence.
She burns Flowey with her fire magic, because she thinks he is a danger to Aliza. Then she leads Aliza to her home, and bakes Aliza her signature butterscotch cinnamon pie, which she had poisoned in an attempt to keep Aliza with her and causes Aliza to become ill. Then she puts Aliza in a bed, and tries to find some medicine.
After Aliza brings Flowey back to life, she comes back. She learns of Aliza's betrayal in bringing back Flowey. Toriel tries to fry Flowey (again..), but Aliza protects him by blocking the way. Toriel becomes angry and attacks and drugs Aliza. Flowey escapes Toriel and Aliza is recaptured. After that, she talks with Sans for a while and comes up with a plan to stop Aliza from escaping.
Then Toriel finds where Aliza has wandered off with Flowey and the drugs cause Aliza to believe Toriel is actually her human mom. Toriel tries to walk away with her, but Flowey cures Aliza, so she can think normally again, and she runs away with Flowey. In front of the door, Toriel kills Aliza with Sans's help. After that, Aliza hugs Toriel and she spares Aliza, and decides to let her go.
Sans - It seems like they are still in touch. Sans was the one who told her how terrible is the world outside the ruins. He also tried to help her by killing Aliza.
Aliza - Like in the original game, Toriel burned Flowey in order to save Aliza. She cares for Aliza, even after she escaped, and tried to keep her at the Ruins at every cost. At the end, Toriel let her go, but Aliza had to promise her that she will free the monsters from the underground.
The Souls - Toriel tried to keep them in the ruins like Aliza, but it didn't end well. Each one of them died while attempting to escape. But even after their death, they are still stuck in Toriel's house. They also ruined her plan by helping Aliza escape.