Five Endings, easiest of the three to get all endings. All that matters is who/what you shoot with the Gun. For the first four, once you shoot whatever you shoot, head back to your car at the bottom of the map.
If you need to know how to get the secret boss, simple;
Pick up A GUN WITH ONE BULLET, and head left. You'll see a Mirror. Shoot it. Go back to the front room, and the gun has respawned. Repeat process until Shattering is achieved.

First ending is shooting Amy, first path on the left. Second ending is shooting a Stranger, first path on the right. Third ending is shooting a Deer, second path on the right. Fourth ending is shooting the Fox, second path on the left. Fifth ending is shooting Michael, triggered by getting to your car without shooting anyone or anything else.

3 endings, and each will require a whole playthrough.
Ending One is to make it to the end with Father Garcia surviving.
Ending Two is to let Father Garcia die and finish the Boss Fight.
Ending 3 is the most complicated.

In the graveyard section, once you get the key, you'll notice John is bleeding. Head all the way back to the start and form a pentagram with the rocks, starting from the top left. Please note it might be a bit finnicky. Next is at the church section, you need to eliminate all the demons within the church, then go outside, go north to the scarecrow, and keep your back turned toward the child. Lead them back inside the church, and to the confessional booth. Finally, during the section where you get turned into a demon, go to the screen where the bridge is, but do NOT go under the bridge. Go back down, and there will be a way up that you can take to get o to the bridge. Kill both people on the bridge. If one or both get away, walk toward the edge of the bridge above the tunnel and Airdorf will run you over, also giving you a chance to try again. THEN, during the section where you scare Demons with the light, go to the room containing the key, then head North. There will be a piece of paper to pick up. Picking up this paper will lock you into Ending 3, no matter if Garcia lives or not. I have heard that you don't need to pick up the paper, but better safe then sorry.

If you're wondering why i'm putting the Prologue AFTER Chapter 2 itself, it's because you unlock the prologue only after beating Chapter 2. A bit weird I know, but anyway...

Ending 1 is to get through the entire thing, and at the end after exiting the hatch, follow the child up to the Podium.
Ending 2 is to instead leave the church, go to the corn field, Purify the scarecrow with your cross, go to your car which is now on fire, light yourself ablaze, and run back to the scarecrow before you die from the fire.

Chapter 2 Prologue 666 Score:
OK so at the start, head to the right down the road. Inspect the crashed car. Go right again, then go left and inspect the car again. Go left once more back to your car. Go up. Inspect the scarecrow. Defeat the Demon. Go up, purify the Dog, grab the Note, go up, purify the Statue, grab that note, go up again, into the Church, pick up the note in the first room, go left, purify the Grail and kill the demon, pick up the note from that, go to the hatch room, pick up the first note, go right, purify the Portrait, remember to use the cross on the cultist that runs out from behind the pile, go to the center room, pick up the next note on the hatch, go to the left, purify the Skull, cross on the cultist from the confessional, go back into the center, pick up the next note from the hatch, go up to the Podium, Purify the glass, quickly go back to the hatch, head down, fight the demon, pick up the note on the way back out of the hatch, then leave the Church, go back to the cornfield, purify the Scarecrow, go to your car which is now on fire, get yourself lit ablaze, and then quickly run back to the Scarecrow.

3 endings. Each one will require a whole playthrough.
First ending is to simply play through the game but don't go for any secrets. Instead of entering the Crucible, you seal it off instead.

Ending 2 is the most complicated. At the Hospital, after you leave through the front entrance and the cop runs off, go back inside, get back on the slab thing, and wait atop a message saying Join Us or ride along the left side of the hallway as you upward to the next room.(This was a bug)
Next, at the Apartments, after you Save Lily and do NOT let her die, go to the elevator and repeatedly press 7, until Something appears. Hunt it down and purify it.
Once done, back to the elevator, and input these floors; 1, 4, 2, 6, 2, 10, 5, 1.
Finally, at the section where you have to get the slabs and whatnot, repeatedly go past the picture of Miriam. You will then be allowed into the crucible.

Ending 3 is the easiest. Simply don't do anything. When arriving at a location, go back in your car, every time. UNFORGIVABLE.

One little bonus section, in case ya don't know about it, check the Local Files of the game. If you don't know, go to the Game Page in your Library, click on the Gear icon, click on Manage, and click Browse Local Files. Enjoy!

Thanks for reading! Leave a comment and whatnot if you have any tips you'd like to share with everyone and stuff.

-The Death Angel

Oh, one last thing;
YA GOTTA HAVE FAITH.