Manaetic Behemoth is located inside the factory, which has a locked door requiring a key to open. The key quest will be outlined in a different guide.
Factory Door Factory Door Location
Inside the first room you will see a gnome on a grate, Giwin Mirakon. Say the phrase
“I will test the machine” to him for your pre-flag.
For this event, you will want to split your raid force into two groups. Spiders will constantly run into Behemoths room from two sides and explode once inside. Their explosion sets off a 4,000 damage AE inside of his room. In order to avoid this, the two groups will want to setup outside each door of Behemoths room and kill all spiders trying to get inside.
After about 5 to 10 minutes of preventing spiders from entering, Behemoth will become targetable and you’ll be able to kill him. At this point you will want to have 1 or 2 groups (or whatever is necessary) stay outside and continue killing spiders, while the rest of the raid charges in for the kill. Spiders must be prevented from entering the room at all times otherwise they will trigger the AE and wipe the raid. Once Behemoth is dead, everyone needs to run out of the room ASAP and finish off the aggroed spiders.
Note : Even after Behemoth is dead, spiders will still run inside. In short, never go into his room unless spiders are being preventing from entering.
Giwin Mirakon will spawn again at East door of Behemoths room, make sure to hail him for your flag. This will grant you access to Plane of Tactics!