Felmyst presents plenty of challenges to the average raid. Figuring out where she's going to breathe during phase 2 shouldn't be one of them. Vulajin of Serious Casual (US-Mal'Ganis) presents this brief guide that will teach you how to recognize the movements she makes that give away where she'll be breathing. Music is "Gerudo Valley" by Koji Kondo.
It's often said that Felmyst is finicky and sometimes "jukes" or makes extra movements. This couldn't be further from the truth. Felmyst flies to one side of the fight area right after she finishes her second Demonic Vapor and finds a vantage point, where she will turn to face the raid. From there she will move once to get into a new position. You can predict where she'll breathe with 100% accuracy as long as you don't miss these key movements..