Story related, can’t be missed.
The Green Minion Hive is found in the Everlight facility. You have to take possession of green minions. 13 spawn beside the possession stone and you can replenish them here should you ever run low when inside. Also, if “you” die you’ll regain control of the overlord back at the stone. The vast majority of this quest is completed just with the minions. Upon entry to the Facility you’ll soon come across the Hive and be told you need to open gates to get it out. There is a dark crystal just behind it if you push the 5-minion switch. Head down the broken grating just beside the hive and cross over the wooden beam. On your left will be a room with some treasure chests, loot these and move on down the stairs, you’ll enter the area you saw below when on the beam.
Your greens are invisible when they stop moving, so you’re safe when in the tall grass. If the Exterminator sees you, run. He can wipe out your minions in short order. However, if you place your greens on a guard marker and get behind them they’ll usually kill it for no loss. Directly opposite where you entered this area is another grating, the area behind which has yet more chests. Move up the stairs to the left of where you entered. Use the 5-minion switch to release gnomes to distract the enemy and wait until you can get behind it to sneak attack it to death.
Turn the switch, head to the next area and take out the Exterminator with his back to you. Turn the other switch allowing you to move the hive along. When you come to another blocked gate enter the broken grating and follow the route around for a cutscene. After this you’ll once more be faced with an enemy whose back is turned to you. Kill it and turn the wheel to advance the hive again. You’ll be told that the sentinels need to be taken out. Stop moving the hive or it’ll run into them. Follow the path around and move in through the gratings to avoid their red search lights. Head up the stairs when you enter the second grating to take a sentinel out. Then, head down the stairs to find the minion wheel that opens the gate allowing the hive through. Continue on until a gate again blocks it.
Once more enter the nearby grate and head right for some chests. Then, return and take the left hand path. You’ll find some pots with more greens in them in case you need them. Get behind the Exterminator and kill him. Then, use the grates on the left or the 5-minion gnome switch to attract up the second and kill him. There are also some gold crates on the upper level. Head to the lower level, open the gate, and head through. Following this path around you’ll find the switch to open the final gate blocked by the hive allowing you to put it on the lift, the game will autosave.
Head over the wooden beam beside the lift and you’ll come to a 5-minion switch and a gate. The gate opens up the way to where you started so activate it then head down to the area opened by the minion switch. Take the stairs down, on the right hand side of the large open area (they can be hard to see here). In the next area wait for the Exterminator to turn his back then kill him. Kill the soldiers and the second Exterminator in this area. If you can sneak around to the 5-minion Switch the Panda will take care of this for you. The grate in the back of the panda cage leads to another Dark Crystal.
Open the gate and head to the next area, directly right of you is a 5-minion switch that leads to another Sentinel for you to kill. This part has several Exterminators. Head left through the vegetation to get behind one and release the Gnomes. Alternatively, if you have the patience you can lure them back one by one to the panda. Head through the grate beside the Gnome switch to find another 5-minion switch. Open the gate and head up to the left to find another Sentinel. Head back down and up the steps into another circular Garden area with two Sentinels and an Exterminator. Make a U-turn from where you entered and you’ll see a grate/path (if you entered via the main stairway this will be on your left). Time your run to avoid anything nasty and head on down. If you open the gate it will send you to the area with the earlier Juno Cutscene and holds nothing of interest. Though, if you head up the stairs you’ll find a 5-minion switch to release two Pandas with a Dark crystal in one of their pens. Both remaining sentinels are on this level too so take them out and turn the wheel that lowers the Green minion hive.
Return to the lower level and kill the last remaining Exterminators then grab the Hive and walk out the front gate with it (the gate will open automatically). At this point you can return to your overlord if you wish, though all the minions will also return so you’ll need to go pick up the Hive again.