Rebel Cops

After the "Mine" mission, you'll have a side-mission available to defend the Photo Studio. Enemies will keep appearing for several turns, with there being 24 in total for the level. The best way to deal with them is to have your squad take up cover in the rooms that only have one entrance, such as the larger room on the north-eastern side. The enemies will flood towards the room, where you can simply take them out with chest shots to immobilize them quickly.