Main Hall, Scorpion Key, Shotgun
Threat level here is low- nothing's going to attack you until a trigger moment upstairs, so explore at your leisure. There is, for example, a very-hard-to-miss Mr. Everywhere bobblehead here (ignore the note, you can still slash him), and an Antique coin in a drawer underneath an angel figurine.
You'll also want to read the newpaper about twenty missing for a Details entry.
There's a shadow-puzzle room here, but we don't have the key yet. Still, you can play around with the system using anything in your inventory. Trying this out nets you the 'Nice Try' achievement.
Ignore the shotgun niche for now- we can't loot it yet. Instead take a look at the main door. This is another of those unlocked-by-bits-of-sculpture jobbies, which is odd (how does that even work? Magnets?). Still, your quest is clear- three heads for the Cerberus door.
Kick things off by grabbing the pendulum from the nearby clock (by the Scorpion door)
Didn't we see a clock without a pendulum earlier? If you've forgotten, there's a hint carved on the pendulum itself, but either way hike back to the den and replace the missing pendulum to yield a White Dog's Head. You may want to check the time as you do- it'll come up later.
Immediately return to the main door and press it into place, freeing up precious inventory space. Go up the stairs to find grandma waiting for you.
She seems harmless enough, but you'll notice that Ethan is unable to stab or shoot her. Which- it's not like he normally assaults the elderly, I'm sure, but these are exceptional circumstance. Hm.
In anycase. enter the door to your left, then bear right out to the balcony.
Hard to believe there's none of this trelliswork that Ethan couldn't kick through, but ignore such doubts, and instead stab apart the box at the balcony's end to score some ammo. Turn left to go inside, and note that you're at the top of the broken stairs by the laundry room save point.
This an ideal place to give pursuers the slip- you can't use the stairs themselves, but the gap in the railing will allow you to drop down to the lower floor, just a few yards from safety.
Grab some chem fluid from the drawer to your left, but do not enter the bathroom on your right just yet. instead follow the hallway, grabbing a Herb from another small end table, and then entering the rec room.
This room has a ton of stuff - gunpowder in the trash can, a second dogshead inside the fat book by trashcan, and even a Mr Everywhere and an antique coin right next to each other.
There's also another glimpse of shotgun, but it's past a door we can't bypass now, so instead turn your attention to the videotape and player in the center of the room. Unlike the last tape, there are no tangible rewards for this one, but it does grant some insight into the next area, and the 'Can't Catch Me' achievement. If either of those intrigue, pop in the tape.
Warp into the (pretty recent) past, and find yourself in Mia's shoes, trying to evade Marguerite. Rush across the bridge and through the double doors.
The open door to your right is just a taunt, instead bear left, and through a couple rooms filled with mold and televisions.
The candles start to go out as you reach the far door, but they aren't directly threat-related. Note the crate immediately visible as you exit the TV room.
As soon as you pass it, Marguerite will enter the corridor from the left. Sneak back behind the crate until she's passed through the right door, then sneak left, the way she came in. Go past the shadowy plinth on to the balcony and go right, hiding in the corner until Marguerite has come and gone (the lantern she carries makes it easy to track her position without getting in her sights).
Return to the plinth and turn the shape so that its shadow matches the spider on the wall. Press F when you're close as you can get, and the wall opens.
Scoot through this narrow passage into a new area. Note the small pile of pallets and other miscellaneous refuse ahead of you. When Marguerite inevitably comes in through the far left door, hide behind this stack. Keep it between you and her until she moves toward the door you entered by. Sneak forward then turn right, dropping into the hole here.
Follow the tunnel and examine the objects here, which will trigger a sudden darkness, ambush, and Mia being dragged off to some gruesome fate or another. She does get to kick Marguerite in the face, which is nice.
Despite the ending, making it this far in the tape does unlock the 'Can't Catch Me' achievement. Return to the present. Dash downstairs to place the second dogshead, and clear out a few inventory spots in the laundry if you need to, then go back upstairs and head to the bathroom.
The bathroom has some important items. There's an antique coin in the toilet, for instance.
Since you're already slathered in filth, you might as well drain the bathtub too. This will yield a Wooden Statuette you can use to solve the shadow puzzle in the Main Hall. Grab the handgun ammo from under the sink, and get ready for action as you open the bathroom door.
Jack appears, and he's happy to see you (how on earth are his glasses still intact?). He'll toss you around, but once you have control just let him chase you around the tub until you're near the door, then sprint for the hall, go left, and drop down the broken spot in the railing we looked at earlier. Land, and sprint for the safety of the laundry room. Even if you stand there with the door open, Jack can't see you while you're inside. Unfortunately, he tends to take up a position by the oxen door, and you need to get back the main hall. The best strategy is to get him to chase you to the laundry room, then wait for him to start searching the kitchen area before making your move.
Shortly after you re-enter the main hall, you'll hear him give up the search. Use the wooden statuette with the plinth, and match the shadow to the shape.
Shimmy through the gap in the wall to reach a hidden trophy room
There's some reasonable loot here- ammo in a drawer and in a destructible crate, chemfluid in the fridge and psychostimulants on the table. There's even a Mr. Everywhere in the nook by the crow door.
In the next room (through the wooden door near the toilet) is a large card table. Check the ashtray for an antique coin.
Read the notes around the room, and ignore the red metal container. When ready, head through the moldy door, which leads into a moldy room.
Soon a moldmonster will detach itself from the wall. They're pretty ugly, but neither quick nor bright. Lead it back to the trophy room, circle around the table/couch island, then run back to and through the mold room. Left into the hall, then right, then right again past the stairs will land you in a new safe room. They really are the best.
Offload all excess gear, but keep the gun, ammo, and a slot of healing items. Get ready for battle, and then exit the room and go down the stairs you just passed.
You're going to run into a couple moldfolk here, and you're going to kill them. Some could be evaded, but it's better to take them out one by one then get ambushed by several later on. The key is to trigger the encounter, then move backwards, applying headshots until they fall.
This can be trickier than it sounds- despite an overall slowness, the mold monsters are forever swaying and lurching about. But you've got a good length of corridor to lead them down, so take your time picking them apart. Remember that you can run and reload at the same time, if you reach the end of a clip unexpectedly. If you're really having trouble, you can kill one, dash upstairs and save, then come back and kill the next, etc. The old ones will stay dead when you do.
The first white door in the corridor leads to the incinerator room. Look around if you like, but don't open the incinerator doors yet- we'll be back for that mystery.
Go further down the hall to see a steel door and a greenish barricade. Absolutely do not open the steel door. Instead, activate the barricade to slide it open. This room has some good stuff but start with the map on the shelves here. Immediately after snagging it, look left to see a hollow in the wall next to a wooden pallet. There's an Antique Coin hidden here.
Loot there other goodie here, including ammo in the crate, some crafting ingredients, and a photo of the fireplace hinting at secret treasure. In the center of the room is the real prize, however- the Scorpion Key, stuck into a bag of... something.
Another mold thing will try to ambush you as you leave. Loop around the table here, either to make a break for it or simply gun it down.
Unlock the brass-like door near the entrance of this room to emerge near the stairs.
There might be one more mold-goon to destroy, but hopefully you're getting the hang of putting these jokers down. If not, trigger it, then loop back the way you came, back up to the saferoom. Manage inventory, then make for the Scorpion door that's past the stairs and right. Yet another mold monster appears here, putting the breed in severe danger of overexposure. And, if your aim is true, extinction.
Open the door, and head to the Rec Room across the main hall. Approach from the balcony side and slowly edge up on the Scorpion Door. This will trigger an entry by Jack. Luckily, Jack is about as savvy as a Moldman when it comes to tables. Circle this one until you're ready to shoot. Jack's motions have a lot less wiggle than the moldies, so you should have no trouble hitting him with a series of headshots. Remember to hit the aim key (right mouse button by default) between shots to ensure maximum cranial trauma.
Of course, he won't stay down forever, but it's long enough for you to unlock the Scorpion door and loot Grandma's room. You can recoup some of the ammo you just spent in Jack's amygdala, but the most important item here is the Broken Shotgun you saw through the glass before.
Grab it and go back to the Main Hall, first floor, and into the shotgun niche here. Grab the real shotgun, and replace it with the broken one. Stride through the open door, shotgun in hand, ready to show these primitive screwheads what's up.