Undyne
Undyne is the head of the Royal Guard and a major Waterfall boss in Undertale.
Encounters
Undyne chases you through Waterfall with spear volleys and a green SOUL spear-block segment. Persistence and pattern reading matter more than LV on peaceful runs.
Friendship path
After she collapses from heat in Hotland, pour water on her, then complete the house hangout with Papyrus’s help. She later trusts you with a letter for Alphys.
Route variants
Genocide transforms this fight into a much harder form. Keep Pacifist and Genocide guides separate in your head.