Start by making a new custom character class. Dump all your karma (evenly) into charisma, summoning, and spirit control. Most important, when you choose a totem, pick the Creator Idol. Don't worry, having no other combat ability is fine. If you're worried, put a couple of points into body and dodge.
Game starts, pick whatever gear, you probably wont be using a weapon. Kill the 3 dudes in the main "lobby" area. Then kill the 4 dudes in the next room. It MIGHT be possible to get the achievement here, with the summon spot in the second room, but you'd have to run through a gauntlet to get to it. Not advised. Proceed to next room where SPOILER Monika dies.
At the start of this room, there are two dudes, kill them both normally, then use the terminal with your character. This starts the 10 round countdown. Gather your team near the "north"/top of the room and use the summon spirit thing on the wall.
There should be 4 dudes (drones count) in the room, plus the big ork dude. The first turn where you have control of your spirit, take the normal 6-7% chance to lose control for the 4 action points. Murder some dudes. Use Dietrich's Haste on your character, and follow your spirit around. On subsequent turns (not the first), use your Creator Idol power so the next bids for AP have 0% chance to fail.
Proceed to murder the dudes. ignore the big ork. After you kill the 4 other dudes, another drone will come through the northwest door. Murder it and the achievement should pop.
Victory.