I'll be covering:

• Vent skip
• Gym storage safe clip
• MB2 skip
• Early key card
• Early rooftop
• Early valve handle
• Stage lighting clip

• Some alternate strategies

I'll try to update the guide as new things are found.

VENT SKIP: Place ladder in specific spot, climb up the side, hold right + shift, crouch through the window. (Help with optimisation from KSaladP.)

GYM STORAGE SAFE CLIP: Climb up the chair, run to the table where the safe is, crouch, hang left while walking forward to clip in, grab the chemical solvent, and run out. Note: Mounting the chair as fast as possible can be tricky. If you click early, a longer animation plays. To get the fastest mount, run right up to the chair, stop for a split second, then mount.

MB2 SKIP: (Timestamp: 6:08) After passing the signs on the wall to the right, you'll enter the corridor where the infinite loop starts. However you can squeeze past the hitbox if you hug the wall as shown in the video. (The condition for passing the hitbox is actually just moving through it sideways - your physical position relative to the wall doesn't actually matter. You could run up to the hitbox and then sidestep through it, but the wall acts as a good set-up).

EARLY KEY CARD: Crouch on a specific step, clip through the glass, push against the step in front, hold left, land on the left side of the bannister below to avoid damage, run forward. (You can do this a bit faster if you skip the part where you push up against the step in front of you, but you have to take extra care to avoid the cutscene hitbox).

EARLY ROOFTOP: Part 1

• After viewing the rooftop key, run back up the stairwell to where the rooftop door is. Make sure you are running so that the janitor is alerted.
• Run against the windows to the right of the rooftop door until you see the janitor slightly turn toward your direction, rather than directly toward the door. This ensures he enters the door in a specific way which is the fastest.
• After you notice him turn toward you, crouch where you stand, paying attention to the janitor's location. If you did it right, he will walk up to the side of the door, 'open' the door, then begin to clip through the wall instead of walking through the door.
• As soon as the door begins to open, clip through it and run through. He should despawn after you enter. Part 2
• Now you will have to follow a specific path to the other side of the rooftop in order to collect the talisman. Usually you would use dowsing rods to indicate the path, but you'll have to learn it here.
• Firstly you can damage boost your way to the right side of the rooftop if you run at a specific angle. Simply run off to the right, aiming just to the left of the intersection between the wire fences, and don't stop running. Look at where I aim in the video to get a better idea.
• Then hug the wall and run forward until reaching a specific tile on the ground (use the orange symbol on the ground as a reference point).
• Turn left sharply and run until you get to another spot on the left side of the orange symbol.
• Now you'll have to run up the curve of the symbol in a specific way, coming to a stop 1 tile beyond the top of the symbol.
• Finally, turn left and run about 3-4 tiles, then turn right and run to the wall, then right again to the talisman. Pick up the talisman and open the door to leave.
• Messing this part up can cost you a lot of health. If you mess up at the end, you may die. Try practicing it first! Save the game just before the cutscene showing the rooftop key, and use that save file to practice. (Timestamp: 8:11)

EARLY VALVE HANDLE (Door clip method): Run across the railing, make a sudden left turn toward the door, crouch briefly and fall through the top. Then run into the door on the right, look into the pile of gym mats, and grab the valve handle inside.

STAGE LIGHTING CLIP: (Timestamp: 11:19) You can clip through the stage lighting at the end of the game. It can be hard to get it consistently. Often what happens is you get forced into a crouch position, and then you need to run out and try again. Basically, just run at one of the lights at a specific angle, and then turn the camera to the right a bit to 'glide' through.

=== Alternate strategies ===

FASTER VENT SKIP: (Timestamp: 0:38) There is a slightly faster way to do the vent skip, but it's much less consistent right now, so I don't recommend it. You have to place the ladder roughly diagonal to the window (hang left a bit before placing it so it doesn't get stuck on the wall). Then climb up holding right and shift, like the other method. Once you reach maximum height the character will walk forward slightly, which is different. Right after the character stops moving forward, you will regain control. Immediately turn right so you are directly facing the window, and then switch from holding right to holding forward, making sure you hold shift the entire time. Then crouch through the window as normal. I do it in one of my runs, 38 seconds in. Pay attention to the input display:

SAFER ROOFTOP ENTRY: (Timestamp: 8:05) Instead of hiding behind the door, you can hide in a corner behind a wall, then crouch past the janitor as he walks by. (Use the angle his light shines as a visual indicator for when to start moving). This is a more lenient way of entering the rooftop because you don't have to worry about clipping through the door, but it is slightly slower.

EARLY VALVE HANDLE (Railing method): (Timestamp: 12:36) This method is about 5 seconds slower.

FASTER ROUTE TO CONTROL ROOM (For Any% So-yeong route) (Timestamp: 10:23) This is probably faster than running the normal way, but I'm not 100% sure. Run off the top of the projection booth onto the railing, then run around until you reach the right side door. Fall backwards off the railing, then move forward in mid-air through the top of the door, crouching briefly to clip through. Make sure to wait a fraction of a second in mid-air before moving forward, otherwise you will get stuck on a bit of geometry that will make you miss the door - then you're softlocked.

[06/11/21] ALTERNATIVE GYM STORAGE SAFE CLIP: This version of the clip is more difficult to perform, and there's no reliable set-up. With a reliable set up it could be 1-2 seconds faster, maybe. For now try to follow the movement / inputs. This is probably the best alternative for playing on the latest English fan patch, where the chair in this room has been removed. (If it wasn't clear in the video, you can grab the chemical solvent in the safe from inside the gym mats.)