Right before the spinning white pellets make contact with the Your SOUL, a fireball appears next to Flowey and knocks him away. Your is instantly healed, and a large goat-like creature comes over.

Toriel: What a terrible creature, torturing such a poor, innocent youth. Ah, do not be afraid, my child. I am TORIEL, caretaker of the RUINS. I pass through this place every day to see if anyone has fallen down. You are the first human to come here in a long time. Come! I will guide you through the catacombs.she says