Egregious is a main mob that splits intermittently. You have to be in melee-ish distance to hit him. He has a hefty pb nuke,so anis are not much good since they have to be in melee distance for the shrooms to hit and then they get ae'd and the shrooms just die.
I recommend anis shrooming behind the encounter somewhere and then pulling adds to the shrooms when Egreg splits.
The main mob is a focus pull. If anis have power, they can spam low level wisps to up the hit count.
Drops a one-time drop ring. I would imagine he drops Mythirians, but we didn't get any.