Easy tank and spank. Summons braziers with different colored orbs. As the fight progresses, named mob's scales will turn a color (orange, green, purple, silver). Drag named between the two braziers that will make the corresponding color. When the next color is called, braziers will turn into adds. Can ignore or AoE down.
Note: After defeating Rhag'Voreth the room immediately fills up with water. You will have some time to get to the air bubble. It is suggested to have a water breathing buff.