I figured something has to do with the mirror, thanks to SCHOLAR tag. Some kind of disabling the boss, I'm sure. I pan the camera, and spot the battery slot on the back. I don't have invis potion on me, so sneaking to the back was fairly intense. I was spotted just before reaching the slot, but my Rogue has big movespeed, and with all the mirrors already aligned, his full starting turn is spent setting up the permastun beam. Then the GG goes "autobots, release me!" and I went all out on Aero source skills on the minions, finally leaving the GG permastunned for the last. P fun fight.