You'll meet Regalla pretty early on in Horizon Forbidden West. She's one of the main threats to the West and Aloy will be working to stop her killing everyone and taking over. You won't actually get the chance to fight her until late in the game. If you're struggling with the Regalla boss fight in Horizon Forbidden West, we have some tips to make it easier.
There will be some spoilers for a late game quest in Horizon Forbidden West below, so don't read on unless you've reached the Regalla Boss Fight.
The Regalla boss fight takes place during the Wings of the Ten quest, after Aloy has gained the ability to fly on Sunwing machines. After saving the Tenakth leader, you'll take on Regalla in a final face off. It can be a pretty tricky fight.
Regalla Boss Fight in Horizon Zero Dawn - The Basics
The fight against Regalla is split into a few sections. As you do damage to clear about a quarter of her health, a short cutscene will play with her getting angry before the fight moves to a different part of the arena the fight is in.
The final section takes place in the open arena you fought a Sliterfang in early on in the story, but the way to defeat Regalla is the same throughout the fight. She does start using some different moves as the fight progresses, but you just need to do one thing and one thing only.
Headshots Only
All you need to do to defeat Regalla in Horizon Forbidden West is aim for her head. Don't use any weapon other than your bow (Hunter Bow is the best to use) and fire shot after shot at her head.
At first, you won't do much damage, but it's worth it once you break her helmet and expose her head. It'll feel like a waste of time and arrows at first, but keep going.
After maybe 10 direct hits to the head, Regalla's helmet will break and you'll then be able to fire more shots at her head, doing a lot of damage each time.
With shot after shot hitting her face, you'll do 100+ damage each time, whittling her health away really quickly.
So that you're making the Regalla boss fight go by as quickly as possible, we'd recommend using Concentration as much as possible. Slowing down time will help you be more accurate with your bow shots to the head.
Other Regalla Boss Fight Tips
We'd also recommend starting the fight with Acid arrows if you have them. They'll weaken Regalla's defenses and make it easier for you to break the armor on her head. Once you've exposed her head, just use standard arrow (or Precision ones if you have them and can stay at a safe distance to use them).
After arrow after arrow to the head, you'll defeat Regalla. Fighting her in any other way will take a lot of time, so stick to this and you'll have no issues.