After you gain control as young Joe, Press esc, Turn off auto save. (This must be done in one sitting, or remember to turn off auto save every time you open the game, if you already have an auto save, delete it)

Throughout the game try to pick the responses carefully as a generally good person, who faithfully loves their spouse, and is willing to mend their fractured relationship by coming to grips with their own faults instead of denying them.

If your going for the bad ending, try to be the biggest, masochistic, psychopath, prick possible.

Anyway the prologue is pretty straight forward, after choosing not to pick the flowers, ivy is happy. (Can’t say the same about Susan’s baby though. Given what is about to happen)
Save game, say that you like cats, if the cat runs away from joe. You get an achievement.

Finish prologue for another achievement.

Main menu:
Go to extra, find “lucky dip” concept art. Another easy Achievement earned. Also turn off hints in the options menu.

Beginning of the game:
After arriving at the hotel but before talking to ivy, QuickSave to slot 1. Walk to cat painting, pick up free magnet, follow ivy to dining room, try to be nice, but you “can’t see” what she’s talking about, leave the dining room, chat with the suddenly appearing receptionist, room 101 key, talk with ivy, be sincere. “I still love you”
Save game in slot 2, reload slot 1, be a jerk when talking to ivy (achievement unlocked) load slot 2.

Walk far right, Enter building, open cabinet, examine cabinet, take book, examine/open book, obtained screwdriver, walk to apartment mailboxes, use screwdriver, take letter, examine letter, obtained key and coupon, walk to basement door, use key, go to basement, open furnace door, continue to walk left, pick up cat clock, walk back. To save time, Don’t even bother running from axe man. Take two steps back, then walk forward and give him a hug. Joe wakes up.

Not much, talk with the receptionist, moving on.

You’ll find a Black Cat, follow the cat, notice the painting by the stairs as your somehow teleported to the second floor after following the cat to the far right. Remembering the painting is important because in the next room is a bunch of doors, look at the mirrors above the doors, if the image in the mirror is the same as the painting, then it is the correct door. (Be careful, The painting is random each playthrough) Through the correct door is a TV. Examine it and now you're playing as Joe in the TV. Through the door, your back in the apartment basement, put the cat clock in the open furnace (you’ve probably been wondering how did 2 items from your dream, end up in your inventory after waking up?), walk to the far left to make the cat run past you, walk back to the right, have a staring contest (you win), in front of the furnace, open the door again then use the magnet to pick up the key. Walk to the far right.
well that was trippy.

Firstly, go back to room 101 to find 1/3rd of a letter. Achievement earned. Then go back to the hallway and unlock room 102. Chat with Sophie. Don’t be in denial.
I don’t think you should look in the mirror. (Not sure if it counts as a bad decision or it's just a short cutscene for exposition) anyway you reluctantly agree to Sophie’s request, go downstairs and answer the phone. Elevator opens. Go to floor 3. Walk to the far right, Open the bathroom door, pick up the syringe on the floor, you could talk to Sophie #3 or just ignore her for now. (The shotgun is a red herring, don’t even bother)

Take the elevator to floor 2, where you talk to the receptionist again, continue walking right until you reach a hallway with large windows, take a couple steps and stop either when you hear whispering or just wait for 30-60 seconds and suddenly gruesome images appear and so does part 2/3 of the letter (achievement earned), continue walking until you find a cigarette vending machine on its side, set it upright and use your coupon from your inventory. The machine is jammed until you find a second coupon but doing this now saves time. So until then go back to room 207, take the glass bowl on the floor, and save your game.

He’s full of crap, but do his little errand anyway.
Go back to the elevator, select ground floor, go upstairs, open the cellar door, in the cellar you’ll find a bottle of castor oil to take, check the chef’s uniform and search the pockets to find the kitchen keys, turn off the lights, leave the cellar, go to the dining room, use the kitchen key, in the kitchen, examine the pig on the table, take the ice pick, continue left to the freezer, tell the pig about your relationship problems, then open the fridge near the exit door, use the ice pick, use the glass bowl to fill it with ice, go back to the cellar, go down the trapdoor, flip the gas lever to the ON position, then examine the body on the table, open up the forehead and you’ll dive into a straightforward flashback sequence.

After all that, remove the brain using the bowl, then examine the cabinet to the right, it doesn’t matter which bottle, use the syringe,
(As soon as you look at the bottles, Joe’s main focus is delivering the poison to Sophie so that’s why you should get the brain first just to save a lot of time) with both items in hand go back to room 102, give the syringe to Sophie but REFUSE to give the injection. What comes next is quite messy. Don’t forget to pick up Sophie’s dress on the chair. Take the elevator back to room 203.

First of all save your game, then give Doctor Z the brain. Pick the first or second option, then tell the doc he’s full of ♥♥♥♥ (again) and you haven’t been listening. This will make him really angry and leave the room, well screw him you can do this yourself. Achievement unlocked. (Reload your previous save) pick anything besides making him angry, flip the lever, and the rest is simple. Give her the dress, be nice.

She wakes up, open the window, talk to moose head, open the door, pick up blanket, turn on radio (achievement unlocked), go to the bed, option 3, go to moose head, use blanket and bed throw, climb out window. In the courtyard, get up and walk left, the camera changes angle, now on your left is a door which is locked and to the far right is a gate, examine the gate, then examine the car in the background, move closer, the camera angle rotates again, walk to the right, push over the statue, it breaks, examine the fragments, pick up “option 3” (achievement unlocked), walk left back to the car, open the door, turn on the engine, use statue fragment, and Agnes has the worst luck. The walk very far to the right through the woods, you’ll find a public bathroom, go to the corridor to the north, take the doll on the floor, leave the bathrooms the way you came through the woods, slender man Easter egg (achievement unlocked), go back to the bathrooms, and continue onward, I apologize for the incredibly vague instructions but the bathroom maze isn’t that difficult, but you will find a hallway with mesh windows, after walking to the right, take another right and continue until you find a room with pumpkins, smash the pumpkin and use the doll on the remains (it’s the only things you have in your inventory, so sure why not.), back track past the hallway with the windows, (axeman walks by in the background, but don’t worry he’s not actually wandering around, and he won’t hunt and kill you either, he’s just there. You can even walk right up to that scripted jump scare to find out he’s not on the other end of the corridor at all, but when you return he’s frozen in place like a poster at the end of a tunnel) anyway you’ll find ivy at a school desk, she will tell you what to do next, but convince her to go with you (just be really stubborn about it, and achievement unlocked), go back down the hall with the windows, then go right, down, and far left to reach a red doorway drawn on the wall, use to bloody doll to create a physical doorknob, enter the passage.

Your separated from ivy and forced into a hall of mirrors, it doesn’t really matter what you answer, but you’ll meet an old lady in the next room (save game) insist on getting her to reveal her real name, there is no way Agnes drinks the soup no matter what you pick so bluff and say you’ll try the soup if the old lady says her real name (achievement unlocked), save game, blow out a candle for another achievement, the reload your save, ignore the candle, then turn back to the dining room and pick up a fork from the table, near the door is a loose floorboard, pry it with a fork to find a crowbar, take the crowbar and go left two rooms, to find a coffin, pry it open with the crowbar.

Joe is having a happy flashback to the last time he and Ivy talked, (Edit: to get the true bad ending, you will have to dismiss Ivy's disorder TWICE and it might be something as simple as saying the same line twice. It took me 5 additional playthroughs to realize where I went wrong) but to get the best ending... do not dismiss Ivy’s eating disorder, name your cat Lucifer. the rest is incredibly straightforward, once you find the gun take the quick way out and Agnes comes to the rescue. This ends the longest part of the game.

Agnes wants to know what her purpose is in all of this (don’t say “no clue” or a small role like saving Joe from the coffin), upon Exiting the maggot house, you’ll end up on floor 4 of the hotel. Quick-save your game. And starting with the beginning, tell Agnes everything.

Choose your words carefully as Joe explains why they checked in, the argument, the Sophie’s (do not try to justify killing them based on their looks, it’s because they took ivy), the mirror, Joe must come to grips with his faults, then you tell Agnes everything else like the cat, her brain was from a dead man, and the receptionist is really horny towards Joe.

After being honest, Agnes trust you.

Walk down the hall and eventually you’ll find a piano, move the piano, then examine it and keep playing until Joe finishes the song and his trip down memory lane.

Near the piano is a room, go through it and you’ll end up in what Joe call his and ivy’s “dream house” with a car and everything, enter the house and go to the kitchen, you’ll find a jar of weed (you don’t have to lie to Agnes about what it is), you could head into the next room but nothing really happens (remember this is where Sophie #4 is) so go back to the piano at the hotel, continue right and enter the elevator. (Story related achievement unlocked, for exploring all hotel floors)

Since you now have a party invitation, go to floor 3 and walk to the right. In the next room talk to Sophie #2. This causes Harrison to appear. Do not agree with him, and tell him to f*** off when he ask for a cigarette (achievement unlocked). Check his coat pockets, then have Agnes distract him while you check the coat pockets again to obtain his room key. Stop Harrison from harassing Agnes. Then go to floor 2, go down the hall to the north to reach room 203, unlock the door, examine the desk dresser, the book to obtain a clue, and the drawers to obtain some tape and a coupon (told you it would save time in the long run). Go to the cigarette vending machine, obtain the cigarettes, go to floor 3, examine the Michael Jackson painting and cover the eyes with tape.
This unlocks a secret room.

After entering, walk to the left and enter the next door with a dead body looks like the doctor, (*puts on shades) is out.

On the floor should be part 3/3 of the letter. (Achievement unlocked), take the buzzsaw from the doctor’s head, save game, and head back to the kitchen freezer, and use the buzzsaw on the pig.

(Context: because if you turned on the gas stove on floor 3, the body in the basement switches the gas valve OFF, going back to the cellar the body demands in bloody writing that you give it’s brain back, Agnes highly disagrees, so plan B is to cut open the pig and put the pig’s brain into the cellar body so it doesn’t F*** up the trap for killing two birds with one stone.)

Pick up the pigs brain (because apparently joe isn’t disgusted with carrying a pig’s brain in his pocket now but was disgusted when he had to transfer a human brain a couple hours ago and needed a glass bowl. I guess it’s a symbolic character moment showing that joe doesn’t care about keeping clean anymore which is symbolic towards the whole DOWNFALL into madness/ denial/ regret.) and give it back to the cellar corpse. Then go back to the floor 3 gas stove and turn it on, give Harrison the cigarette and watch the events taking place. Your then given the opportunity to deliver a epic one liner.
Choose whichever one you want :)

Investigate the remains of the exploded bathroom to find a room on the far right, on the table is a head and a note, take both, and exit. The smoke clears in the bathroom and pick up the lump of fat on the floor near the stove. Go back to the kitchen and save game.

Examine the recipe in your inventory.
Pour the castor oil into the pan that’s near the blender, also pour some oil into the blender, back in front of the oiled pan, turn on the stovetop, put the fat on the pan, and put the head in the blender, be careful how you justify this to Agnes, pick up the fat from the stove (then Agnes will give you the fork she got from loralai’s house), put the fat in the blender, put the weed into the blender, put everything else into the blender just to make sure then turn it on. This triggers a cutscene as the blender hums to the rock music, Agnes is disgusted and leaves, joe tries to comfort her.

It’s disgusting but Agnes understands that your doing this to save your wife. You pick up the blender’s smoothie and head for room 203 on the second floor. (Why? Because on the third floor Sophie #2 is gone along with half of Harrison’s dead body, so Joe and Agnes deduce she must be in room 203), just before you enter Joe hallucinates, try to honestly answer Agnes, then enter 203, you can play along with Sophie #2’s fantasy (it’s fine, Harrison’s just dead tired.)
Either way you give Sophie the smoothie and she quietly throws up her organs on the floor. Leaving room 203 is the receptionist again (long time, no see.) she invites you to her office on the fourth floor near room 666.

In her office she will prove the morality of you actions and ask your to be on her side.
Refuse the offer. Agnes is happy.
The receptionist leaves and playfully teases you by leaving clues eventually leading you back to the kitchen freezer. After entering the new passageway, examining the article of clothing on the floor unlocks an achievement.

This next segment of the game will test you on being faithful to Ivy and trust in Agnes. Save your game. AXE AGNES, AXE RECEPTIONIST, leave room, enter manager’s office, Agnes head is on the desk. (That’s 3 achievements unlocked in a row!!!!) reload save.
Kill the manager.

One Sophie remaining, you’ve got an axe, you know where she is. GO. Joe marches to his dream house, the end is near. Upon reaching the Living room, Sophie #4 seems to have run away. You stride to the right, open the door, it’s locked, break down the door, joe marches down the hall and into the light. The stability of his happy place is rocky, he enters quiet haven once again, finds a present, and ditches the fire axe for something more...efficient. A chainsaw. (Achievement unlocked).

Noisy neighbors:
Meanwhile Susan ashworth, wakes up and exits her apartment flat to investigate noises from across the hall.

He takes his chainsaw to the basement when Sophie #4 is. Use chainsaw. (Achievement unlocked.) enter the mirror. Walk to the left.
Cutscene....... ;(
But there is still a shred of hope as joe remembers the electric chair. It’s a risk but it’s your only choice.

Back as Susan, Continue to the far right until you find a locked cabinet and further on is a length of rope. Fade to black.

Joe carries ivy to the elevator, all the buttons say floor 5. Fade to black.

Back as Susan, Use the rope to climb down the hole near the dining table. Fade to black.

Joe talks with his father, they talk about his little brother, and joe says goodbye. Save game. He places ivy on the operating table but the doctor appears saying “it won’t work”. But in response you say “nothing is impossible” (achievement unlocked), and you flip the lever.

Meanwhile Susan hears screaming coming from the basement, she decides it’s time to craft a weapon or two. Go to the right, pick up the mannequin arm, to the north enter the bathroom, save game, pick up the rag in the pipe, and the blade in the foreground near the door, go back to the rope and go down the ladder, use the arm on the sewage hole to retrieve a key, climb the ladder and rope, go back to the locked cabinet and use the key, you’ll obtain tape, go back to Susan’s flat, use the rag to pick up the glass on the floor, go back down the rope, and walk to the left, open the stove to find a cat skull, close the stove. Examine the work bench, put all items on the workbench to make 2 weapons. Go down the ladder and continue to the right. Pick your weapon of choice. (Achievement unlocked).

Save game
The machine didn’t work, joe breaks down in tears, as characters appear at the doorway.
First being Harrison. “It’s people like you who...”
Next is Sophie. “She saw you..”
“I was just trying to save her”
Next is Robbie. “I’m so sorry”
“What do I do now?”
Instead the queen of maggots answers joe.
“This is not the end.”
And lastly, Agnes. “Your the part of ivy, I fell in love with”.

It’s time to sacrifice Agnes for Ivy to live.
Memories flood joe’s mind with a single goal in mind. Saving Ivy. With his mind at ease, Joe flips the switch. Cutscene. If done correctly (golden ending achievement unlocked, followed by hardcore and auto savior after skipping the credits) result screen 27/27 white cat skulls.

Now play it again from the top, for the bad ending. Prologue and all. just to be sure.
i can't definitively say SPECIFICALLY how to get the bad ending but hopefully this guide worked out okay.