There's gotta be some guide out there until someone makes an actual guide with effort
This is all I know and figured out(assumed)
As far as I know, I think it's all finished

Your ending depends on 2 things, your pact health and red lens caps
The pact you choose only determines your method of maintaining that health
Pact health degrades over time, not progress
The quickest way to get most of the endings is to leave your last save at the one before the spike run (in the picture) and just wait and reload each ending. I recommend R>B>Y ordered by risk (you should save further when you get to the yellow end)
Your weapon filth does not have any known effect until corrupt, where it will halt pact healing
Your ending is finalizing once you toss your weapon away before the gondola ride
Your pact health color will match the ending you get

Divine/Blue: Ending B
Good/Yellow: Ending Y
Bad/Red: Ending R
Red lens caps: Ending A - 6 needed (thx trinity of aces)
With enough lens caps, Ending A takes priority (Ending Y untested thus far)
(More caps may be needed the lower your pact health is, I am not going to test that.)

Use skeleton3000s guide for the caps
https://steamproxy-script.pipiskins.com/sharedfiles/filedetails/?id=3424916190
Idk if there's a safer way to link other guides, so just trust me, click the sketchy link ;)

You can collect Red lens caps, along with bonus content, by going into camera mode and pressing q on them. You will see them hanging in various places
Caps will not appear, nor any other bonus content, until the second playthrough

Ex hard mode and first person mode
4 challenge stages needed for the achievement
6 outfits. Default Becky, Tomoro, Jasmine, Wendigo, Ending B, Student. (thx atromin)
10 Blue caps to collect in total (along with an extra challenge #2 for some reason)

Becky unlocked by default
Ending B unlocked after Ending B and sparing Wendigo (thx skeleton3000)

Epilogue appears after you go through all the endings (and/or S rank all the challenges idk)

Actors: Down Up Down Up Down
Rock maze: Up.
Red pillars: There is a room in the back right with a 3x3 grid of red dots. The reddest dot is the right button.
3 number combo: Blue 9 Yellow 7 Becky 8
Red maze alt: 3 4 2 1


Easiest to hardest pact (imo)
Extermination > Photography > Friendship (a recent patch may have flipped photo and friend)
Extermination you can kill anything when you get low and it decays slowest
Photography uses shots without dealing damage and now you can't use your bat to heal and it decays fast
Friendship you only have so many phones to heal, some are hard to find

Early enemies take one head shot
After they're gone, the majority take 2
One headshot and one melee is generally enough to kill
Healing is plentiful, running past enemies is viable even if you're bad at dodging, more viable than fighting everything
Enemies pivot slowly, you really really shouldn't be bad at dodging

The first boss takes a lot of hits and supplies endless ammo until it's dead so don't bother hoarding ammo until after
4 shots a box, 18 hits to kill, waste ammo at 17 for 3 extra shots after the fight if you're that stingy

Journal search alternative path
Going through the non one way door, once you do the red pillar puzzle, go back to the locked door
Behind it there is a ramp you can walk up and enter a courtyard full of enemies
Ignore them, unless you're good enough to dodge and get the 2 loot by the outer wall, hug the right inner wall until you find the ramp (it's hard to find but it's there)
Get the key and enter the door, Q on the blue wall for a secret top down section
You will get both journal entries but miss some caps in the other section

Silly moment
The part at the end of the one way door where you're pulled in
You can grab the box, float up, and hop on the monsters platform
This does absolutely nothing, it's just fun

Second boss takes 13 shots, kill it in the first long hall where it first appears and stun lock it for easiest time lining up

White space optimized route
7 8 9
4 5 6
1 2 3
2>1 blue button
1>2>5>8>7 yellow button
7>8>9 blue key
9>6 red button
6>3>2>1 eye

That ONE drop part
Go to the end of the path, run toward the top right of the next platform
Stand next to the next platforms top end, walk up right until you pass the platform before the camera change
Grab the health pills, grab the red lens cap, and for some reason, you can press Q to pick up ammo for once on the next platform

Chainsaw monster fight
You can move a wall to block it and get closer to move the camera behind him

Spike run
Before your camera is changed to the vents, you can drag the bridge over then keep walking until your camera switches back and you're right by the door

Drop into first person (hard mode(thx tomos))
There are 2 rooms you need to go into 1 you ignore
After walking through the first door, go to the lamp and enter the door to the left, it will have blinking eyeball faced Becky baseboards
Just follow the path
After you exit, the next should be at 11 o'clock from there, just go around the corners and follow that direction
There will be viney and woody walls
Hug the right, go up the ramp, turn left and press the button
Careful of the enemy below, you can snipe it if you can see well enough
Doing them the other way around will spawn a monster in the door room

Ending B Red cubes and darkness maze (removed I think)
Straight = Pass the fork Turn = You turn despite no fork in the path
Right, straight, straight, turn, left, right, right, left, right, right, left, straight, turn, straight, straight
There should be a cube floating on the left side as you keep walking, if there's not, someone messed up here and I don't think it's me
Left, straight, straight, 2 minute walk

Ending Y, there is a platform with pills on it around the ledge you drop down before the fight that you can stand on and kill the boss without jumping all the way down

Challenge 3
Go up the elevator
Avoid the hatch to the pool


Note: If someone wants to plagiarize this whole thing just to make it prettier and more organized, idrc