Level 13: Cooler
Go to Valeries last known position
Levels have begun in a more pleasant fashion than the Cooler level, which immediately squares you off against not one, but two Fat Boys, in a couple of narrow hallways. The main difficulty here lies in the initial feinting process: you have to manage to get behind one of the Fat Boys so that youre not pinned between them. After that, rockets, grenades, and your assault rifle should make short work of the beasts. Try to stick to the middle of each hallway, and strafe left or right around the Fat Boys rockets as theyre incoming. Leave yourself plenty of room between you and the wall behind you, and you should be fine. If not, theres a medkit by a body near the fuel tanks.
Another little firefight ensues in the next room over, between a couple of Spectres, a scientist, and a merc. The best course of action here is to step through the door leading into the room, which triggers the fighting, then retreat back to the fuel tank and crawl through the ducts, taking the first right turn. Thisll lead back into the room, but you can fire upon the survivors from the duct with less risk of getting hit.
Since a game without quicksaving wouldnt really be quite the same without two difficult fights in-between save points, youre treated here to a duel between a few mercs and a Fat Boy in a narrow corridor. Your best bet here, and its far from a sure thing, is to try and wipe out the mercs first, either with grenades or rockets, then charge down the corridor to grab their minigun and use that on the Fat Boy. Since the minigun is positioned so close to the wall, youll probably want to disengage and take cover before the Fat Boys rockets hit you, then dash out and fire again, repeating the process until he goes down. Grab the keycard and the items from the ledge near the minigun, then head back to the locked door in the adjacent room, which the keycard will open.
Now that youve finally managed to save your game, you can keep on truckin through the now-unlocked door. Take out the Spectres and the mercs here, then turn the corner to get the Tridgens attention. Youll have noticed the vents set into the floor of this hallway; crouching into one of them will get you a fair bit of protection from the Tridgens jumping attacks.
Find the security switch to access the elevator
Beyond the Tridgen hallway, youll enter a room where the mother of all PowerPoint presentations was apparently taking place before the disturbances began. The Locusts and maintenance workers in here are woefully inept at killing each other, so do your best to give them a hand, then head into the Archives room.
The first room on the left as you enter the hallway isnt necessary to enter, but it does contain a box of Jackhammer ammo, which will be helpful when youre assaulted by Spectres farther down. At any rate, as you pass through the gauntlet of foes here, youll eventually arrive at a room of armored mercs and Tridgens; kill everyone and flip the red switch on the wall to activate the elevator. The passage nearby leads you back to PowerPoint room, where the door to the main elevator has been unlocked. Head down, and reload your weapons on the way.
Another firefight is occurring down here, but if you mind your own business and stay out of the way, you should be able to keep a separate peace with the hostile parties. If you skulk your way to the left side of the room, youll come across a couple of mercenaries hiding behind some overturned cabinets. Heres a tip: if youre ever assaulted by mutants with rocket launchers attached to their arms, be sure to reinforce your makeshift fortifications by stacking explosive canisters atop them. This wont actually make them any more secure, but it will help prevent your zombification due to the fact that your body will be in a hundred little pieces.
The room beyond the fortification is another lab - an evil lab. You can tell by looking at the copy of Evil Scientist magazine on the counter. ("Ten great tips to help hide WMDs from UN inspectors!") Flip the switch here to open the doors to the "big tank room." The hallway branching out from the lab will lead you to a position overlooking said "big tank room," and the firefight thats currently ongoing between Locusts and a few mercs. Using your AG36s scoped view and your night vision, you should be able to take down all of the combatants fairly easily. You may want to just shoot the two nearest mercs, then leave the two that are actually inside the room alone, so that the Locusts concentrate their fire on them.
Flood the mutagen room to access the upper floor
When the room is clear, rotate the steam valve at one end to instigate a probably-impossibly-quick flooding of the entire interior, then swim up through the vent at the top. Youll soon be facing off against a single Fat Boy at fairly close range, so youll want to have collected any spare armor that the mercs dropped before you spin the valve here.
This Fat Boy fight is supremely annoying, mostly due to the way his rockets detonate after they penetrate the surface of the water. Theres no easy way to kill him, unfortunately; if you reach this point without enough health, you may have to go back a save point or two and try the previous portions of the level in a different manner so that youre not crippled when you reach him. After you dispatch him and the Tridgens in the classroom beyond, youll finally reach Valeries last known location. And, in a stunning plot twist, shes actually still here, even if she is sharing the room with two Tridgens. Kill them off to end the level, and be shuttled off to some other inglorious assignment.