You had just left Snowdin, and were continuing your journey, But for a certain reason, you felt like you were being followed and watched. You looked around, and when you looked back, a spear stopped in front of you, and a shadow began to approach, and it seemed to be someone tall.

Fell Undyne: "..hey you can't go from here."

a kind of fish woman blocks the way, and she was very intimidating, she was pointing a spear at you, and She didn't seem in a very good mood.