It is possible to separate the Harpy Guardian from all the other enemies. When you get to the boss fight dont charge right in. after you hop up the "steps" inch out slowly. All the other enemies will spawn except the boss. Defeat all the enemies until nothing else spawns then walk out into the arena. Use charged earth arrows. His alternates between a quick rapid fire shot, which can be dodged with one roll. Then he roars and does a huge area shot. When you hear his roar, roll at least 3 times then you will be fine. It will take a lot of charged shots so stay focused.