Soldiers are thrown into the first three sectors at random, meaning they always end up in the plateau to face whichever form of the Freezing Guardian they've summoned. Once in a sector, they must fend themselves off for three minutes for the sector summon portal to appear or wait until the difficulty increases further to their liking. Here are the four sectors:
This outdoors area from Valkyrie Lab features many enemies spawns as they jump out of every sniper nests and others doorways on the ground floor. This sector belongs to Dr. Haze and her minions: Brine Speedilos, Spitters, Bloated Kamikaze, Elite Disaster, Tick Queens and their Kamikaze Crawlers.
Broken Station's plaza features enemies spawning from the side buildings or by dropping off the bridge. This sector belongs to the Destroyer and its minions: Ancient Moles, Mechanical Crabs and Elite Hammerheads.
Fatal Canyon now allows soldiers to go at the bottom via an access ramp. This sectors is where the Poison Scorpion resides, alongside its minions: Fire Speedilos, Magma Demolishers, Mortar Bots and Skull Troopers.
Freezing Guardian. The boss can move from one side to another to keep soldiers on their toes. At some point, the soldiers will get to visit the inside of the beast and be able to attack its heart.