Key mob is a pernicious technomagus can be found Control Room Beta or Control Room Omega. Chest is in Control Room Alpha.
Avoid Taranis Gazerra near the entrance. It's protected by a shield and attacking it will trigger massive damage called Magnified Beam of Disintegration. To disable its shield, you need to disconnect the four beam machines located throughout the instance.
When he says "No! While my power still holds, I WILL NOT FALL!" he becomes invulnerable. Click the machine on the wall to "unplug the contraption". When it disconnects, it will begin emitting an energy beam. Drag the Beam Handler across the beam to remove his invulnerability. Note that you must move him through the beam, so it might take a bit of repositioning by the tank.
You will get a message which shows he is "casting a powerful spell". He will be rooted and starts casting Horrifying Channeling. Everyone, including the tank, needs to move as far away from him as possible. Getting hit with his AoE will curse you for about 100K damage per tick.
Continue to Technomage Grid Mechanic and kill him outside the laser room. The lasers hit for 300k each, so in order to pass safely you must use the 8 mirrors in the previous room and place one in each of the glowing blue boxes in the room.