The Aery is the third dungeon you unlock in the Heavensward expansion. You gain access to this dungeon at level 55. This is the easiest dungeon for grinding experience. In this guide I'll give you details on how to beat the bosses for an easy clear.
How to beat Rangda
Rangda uses multiple lightning based attacks, one of which resembles an attack Anchag uses in Amdapoor Kep Hard Mode. This fight is really about movement and reaction speed. Rangda will also summon Leyak monsters periodically throughout the fight. The Leyak die quickly, so they aren't a huge threat.
Attacks:
Electric Predation: A frontal AoE cleave dealing moderate damage.
Electric Cachexia: A room wide lightning AoE with a safe area in the center.
Ionospheric Charge: Rangda will target three people at random and drop three waves of lighting on them. At this point don't lock yourself in an animation so that you can dodge all three waves.
Rangda will also apply Prey on a target attaching a tether to them that needs to be attached to one of the statues around the room. If you fail to do so in time, you'll take a massive amount of damage and be paralyzed. Prey appears to target whoever isn't targeted by the lightning.
Electrocution: This attack will hit three players dealing moderate damage and knocking them backward.
How to beat Gyascutus
This is by far the simplest fight in the dungeon. The only big thing you need to keep track of is the Mustard Gas adds. They need to be allowed to absorb two of the poison orbs before you kill them to keep the room from becoming too dangerous to move around in.
Attacks:
The Serpent's Apple: This is a frontal cleave that deals moderate damage.
Fall of Man: Gyascutus will place a poison orb on the ground. These will poison players who stand in them. The Mustard Gas adds need to be allowed to absorb two of these before you kill them, to keep the room clear. Gyascutus also gets a stacking damage increase buff based on the number of orbs that are on the field.
Body Slam: A circular AoE centered on Gyascutus common to all basilisk type monsters.
How to beat Nidhogg
Nidhogg is the final boss of The Aery. He has some unique attacks, but overall isn't very complex. If you ignore the fight mechanics though, it will result in death or a complete wipe.
During the add phase, the healer should focus on healing Estinien during the first two waves as the Liegetail monsters are incredibly hard to pull off Estinien. The Liegedrake, Ahleh, and Oskh are simple to tank, but the Liegetail will deal a considerable amount of damage to Estinien based on your group's damage speed. If Estinien dies, the party will wipe. After adds die remain stacked on Estinien for the defensive shield or you will die.
Attacks:
The Scarlet Whisper: A frontal fire AoE cleave dealing moderate damage.
The Scarlet Price: Nidhogg will place fire orbs around the room. The orbs themselves will damage players that are hit with them. These orbs will do a straight line AoE attack before disappearing.
The Sable Price: One of the non-tank players will be target with this, raising them off the ground. During this time that player can't use any actions or move. The DPS need to kill the Sable Price before its cast bar finishes, or the incapacitated player will die.
Deafening Bellow: A room wide AoE.
Massacre: Nidhogg casts this during the add phase. If you fail to kill the adds in time, Estinien will not cast the shield, and you will die. Make sure you get inside the shield. Within the shield, you will only take moderate damage.