Kill or Spare Regalla in Horizon Forbidden West

After defeating Regalla, you can either kill her or spare her life. The third option does nothing.

If you kill Regalla

If you kill Regalls, then you will get her unique bow. This is a very powerful weapon, so I recommend choosing this option.

If you spare Regalla

In this case, Regalla will keep you company in the last battle. You won't get her unique bow, but you will avoid an extra fight with Ghosts.