I will eventually create a walkthrough video but since I will be recovering from surgery for quite a while I decided to write down something first. I'm not sure how extensively I should write this so I'll try to give general instructions rather than detailed explanation. You should scratch your own head and finish the game yourself but if you get seriously stuck you can use this guide (I did not find any other, if they exist they are well hidden).
There are 11-ish puzzles in total, the game saves after each part is finished. If you quit the game in the middle of a puzzle you will have to start that puzzle over as all items will respawn. I tried to name what you have to do according to the achievements. I'm not 100% sure that they are correct, but if you finish the game you will get all these plus 1 for ending and possibly 1 for the type of locomotion you did not use and 1 for launching the game (16 achievements in total).
Time is only a brain creation
The room you start the game features a big clock that hides the way out of the room. In order to get out you need to move the hands on the clock. The little and big hand can be moved by pressing buttons. One is located on the piano (hour) and the other one (minutes) is located on the photo/painting on the wall. The hour that needs to be set can be found in the journal on the table in the corner of the room - 3:30.
Set clock hands to 3:30
After you get out of the room, you will go down the stairs and appear in a room with four photos. There is a possibility to go to the left, so go there and enter the only room there. The only thing you need to do here is light the fireplace. In order to do that put some logs in the fireplace and light them with a candle. A ghost will then enter the room and drop a clue and a new image will show in the room.
Go back to the room with the 4 photos. Here you have to switch off the lights of two photos that you haven't seen yet. One photo is from the first room (with a church) and the other one is in the room you just left with the fireplace (dolls?) Stairs going down will appear.
Friendship never dies
Go down the stairs and grab a crowbar. Break the glass with it. Behind the cabinet there is a vent. You can move the cabinet with your hand or just put your arm behind it. There is a rectangular piece so grab it and put it in the thing that was behind the glass you broke. You will get a key. Bring the key to the two drawers at the bottom of the cabinet. In the upper drawer you will find a screwdriver that you can use on the screws blocking your way through the vent.
Collect some of the handles (weird looking things you probably wondered what they are for) and enter the vent.
You will find yourself inside a morgue where you need to open certain door and keep certain door closed. Apply the clue from the ghost.
1 0 X 1 1 0
1 0 0 1 1 0
Open the door where there is 1 and keep closed the ones that are marked with 0. In order to open the doors you will need handles that are scattered across the rooms. Two are in the morgue, one is in the first room, two are in the second room I believe. When you have that done according the clue, open the door marked with X. Pull the body out - after a little jumpscare you'll end up in a different morgue.
Where am I?
All you have to do in this morgue is to grab the head and toss it where the body was previously stored. Just find the door with the David Baehr name on it. After you do this you will here a ding and the elevator will go down and open. You will be able to choose one of two levels. It doesn't matter in which one you go since they are connected by stairs (or the elevator).
First you need to go to the bathroom (somewhere on the left). You need to let the water flow from certain taps. If you look at the showers you will see that one is working and one does not. So turn the taps that share the side with the working shower. It should be the first sink and the furthest one. The sinks will then give you a combination that you need to apply on the toilet flushers.
left, right, left, middle, middle
When you enter the combination correctly you will hear a sound of door opening upstairs.
Enter the door that opened. You will enter a school. The first door on the right will lead you to a classroom where there is a drawing of man on fire. On the blackboard you will have to draw something. You will find out what that is if you find three pieces of a drawing.
The first one is in this room on a desk. The second one is in the classroom locked in a piece of furniture. The key is in the central room. In the furthermost door there is a child's toy on which you need to put the corresponding shapes to get the last piece of the drawing. Two pieces for the toy are in the same room, but the rest you have to find as well (two are in the lockers, one is in the center room, and the last one is in the classroom in a desk, furthest away from the blackboard).
Draw the man on the blackboard and a word 'WHY' will appear, then you will teleport into a mansion.
The mansion puzzle takes a bit longer than the other puzzles. You will need to find 6 white papers. The first one shows 4 different symbols. The other 5 show 3 rows of 2 symbols. What you have to do is find the corresponding symbol from the starting paper on another paper (it will be on the left). Then look for the right symbol. If you find it again on the left, see if you can find the right symbol elsewhere. When you can't find the right symbol anywhere, that's the symbol you need. In the middle of the mansion there are four marked slots where you can put something which correspond to the 4 symbols you are looking for. They resemble letters H E L L.
In order to get all symbols and white papers you will need to open one closed door. In order to open it you have knock 13 times.
After entering the word 'Hell' the environment will turn into rather hellish one or nightmare one. If you will go back to the three door upstairs you will find out that one is closed and doesn't have a handle. You need to get the handle to open it. There you will find a piece of metal that you will use as a lever in the furthermost room. In that room you need to move the furniture in a way so you can reach the thing where to put the lever and then pull it down. It will open another door somewhere at the clinic or the other accessible floor.
You will enter another school. In one of the rooms there is a rug on the floor that shows numbers, shapes and letters. That is what you will use to figure out the hang man puzzle. The hangman puzzle is again in the class on a blackboard. There are shapes above the blackboard. You will have to find those shapes and their corresponding number. There are 4 clues around the school that will tell you that background is something that will allow you to find a number and thus letter and that sun is a star. There are four shapes - a star that you can find on the walls and has two numbers 1, 1 and 5. Square that is also on a wall and has number 6. Wooden triangle toy is (in a desk in classroom?) 7 and rectangle is 4. What you have to do is look at the rug and check the background color of the shape.
Then count boxes colored this way, you should always lend on a letter. So Star shape will get you R and M, rectangle will get you U, triangle D, square E. Out of these letters you need to find the correct word, the order is above the blackboard, you'll just have to figure out where 1 or 5 is. The correct answer is REDRUM.
You have to write that on the blackboard using the shapes that you can see on the opposite wall.
After a fire you will appear in a new and very creepy location with fetuses in jars scattered around. All you have to do is find the four correct ones and place them where they should be (just check the name tags).
In the last part of the game you will have to find a hammer and get a crowbar behind wooden bars that you can't miss. You will need the crowbar to enter a barricaded door further inside. In the room there is a chair and gasoline around it. This is the place where you will have to lurk a monster that walks around. Before you do this you gotta find a candle (it's to the right if you enter from the entrance). If you make a way towards the room with the chair from the right you will also find a light that you can use to light your candle if by a chance it goes off. The monster walks slowly and will not pursue if you run too fast, so walk slowly. Then enter the room and walk past the gasoline. When the mosnter goes over it throw the candle there and make the monster die in fire.
Killed or Pacifist
When this happens you will find yourself elsewhere watching a man die in fire on a bed. If you walk out of the room a policeman will come at you with a gun telling you to put down hands on the ground or be shoot. Depending on whether you surrender or not you will get Killed or Pacifist achievementThe remaining achievements are Welcome which you get when you launch the game, TP Master if you use teleport locomotion throughout the whole game and Free Man if you used the free locomotion.
Ren (stsungjp on Twitter)