How To Get REGALLA'S WRATH In Horizon Forbidden West (Missable Weapon)
You must complete the main story mission "The Wings of the Ten" until you encounter Regalla.
Once you defeat her, you will receive a choice. Do you want to kill her or spare her life?
Choose "your life ends here" to get her bow after the mission ends.
If you let her live you will get a unique outfit instead but not her bowl.