All mobs in the first room must be cleared before spawning and pulling Aeri'ondi the Infectious, as they will be called to him when the fight begins.
To spawn Aeri'ondi the Infectious, run up the ramp onto the tallest pillar in the center of the room. He will spawn and begin attacking (he can be spawned but will not attack if you run up while invisible).
Periodically, Aeri'ondi the Infectious will spawn an acid pool where he is standing. These acid pools persist throughout the fight. Standing in the acid pools will cause a stacking Noxious Debuff that will do damage over time, and will drain power. This Noxious debuff can be cured, but will stack quicker the longer one stands in the acid pool.
It is recommended that as Aeri'ondi the Infectious spawns acid pools, that all players move out of the acid pool. The tank should keep the boss near the acid pool, but if possible the tank should stand outside of it.
As more acid pools are spawned, you will want to continue moving Aeri'ondi the Infectious over the bridges and islands on the outside of the room.
Falling into the acid lake will grant a noxious debuff that will do a large amount of damage over time. If a person falls in, they should get out as soon as possible and should be cured of the DoT