Trained Employee
Complete the tutorial
Simply finish the tutorial to get this achievement.

For the campaign, with every day, the anomalies will become harder to spot, with more characters to go through each day and there being 5 days in total.
The hats are not considered anomalies.
You can choose to either call the DDD or reject doppelgangers.
Extra tips can be found in the General Tips section of this guide.
Number of characters you'll have to go through per day (assuming no one dies):
Day 1: 5
Day 2: 7
Day 3: 9
Day 4: 12
Day 5: Results

Work Accident
Remove a neighbour
Hit the red button and summon the DDD to remove any neighbour. Achievement should pop at end of day, can be done in Arcade as well.

Got You!
Make a doppelganger reveal itself to you
Once you've identified a doppelganger, do not call the DDD, deny them entry to the building instead. This might take a few tries.

Unlikely
Defeat the clown
The clown will appear every playthrough at least once, don't worry about beating him first try as after you finish the main campaign, he appears in Card Mode. Take your time with the cards, and ensure that your next move is planned.

Better Than Henry
Get an S rank
I recommend doing this on either day 1 or 2. Make sure the checklist is filled up correctly for each resident and ensure that no doppelgangers get through. Time is not a factor so be patient and ensure that the characters are sorted properly. Achievement should pop at end of day.

Hunter
Capture 100 doppelgangers
Obtained along the course of regular gameplay, simply call the DDD on the doppelgangers 100 times. Progress in Nightmare and Arcade is also counted.

Quarantine
Complete 40 matches
Obtained along the course of regular gameplay, progress in Nightmare and Arcade is also counted. If you're farming the doppelganger achievement in the campaign, each completed day counts as 1 match.

Bounty Hunting
Get all the Wanted Posters
Obtained along the course of regular gameplay, posters can also be obtained in Arcade.
This achievement will likely take you the longest to get. I'd recommend doing this by resetting day 1 of the main campaign as you will see at least 1 wanted doppelganger per day.
The wanted doppelganger of the day will always be one of the residents on the entry roster.
If you're only missing a few, here are all the doppelgangers for you to narrow down the ones you're missing. You can compare the image with your own from the records tab in the main menu.
Another way to do this is by following Green Cat's suggestion in the comments section:

1. Make a checklist of your missing characters by comparing your wanted posters to the image below
   
2. Start a new campaign where you eliminate everyone except the characters you're missing (This increases the chances of the ones you need showing up)
   
3. By day 4, most of the residents should be eliminated, making it more likely that the ones you need show up
   
4. Do not proceed to the next day, instead, keep resetting day 4 till you end up with all the wanted posters you're missing

The Best in the Class
Complete Chester's quiz
Chester shows up daily in campaign mode and asks the same questions every time. Simply answer all his questions correctly to get the achievement and a medal.

Just Like Henry
Get this ending in Campaign Mode
Beat the game with some dead residents.
The achievement should pop on the 5th day.

Conspirator
At least you tried.
Beat the game ensuring only W. Afton dies. This can be done by calling the DDD on him and making sure all other residents survive.
The achievement should pop on the 5th day.

6 Feet Underground
Get this ending in Campaign Mode
Beat the game by letting all residents (including doppelgangers) into the building.
The achievement should pop on the 5th day.

With the Right to A Call
Get this ending in Campaign Mode
Beat the game by calling the DDD on every resident (including doppelgangers).
The achievement should pop on the 5th day.

Employee of the Month
Get this ending in Campaign Mode
Beat the game while ensuring that none of the residents die.
The achievement should pop on the 5th day.

There are tips below to help you ensure that all the residents survive in the General Tips section of the guide.

Overtime
Get a score of 1000 or higher in Arcade Mode.
This can be done by making sure the checklists are filled out properly for the residents, and ensuring that the DDD is called on every doppelganger (Calling them gives an extra score boost). There is a time bonus for finishing as fast as possible so try your best to speedrun this mode.
This can also be done by guessing solely based on characters appearances, which is what i did for the below run.

Wake Up!
Complete a match in Nightmare Mode.
This mode is harder than the campaign due to the different facial features. Remember to look out for teeth, stitches, scars, tattoos and horns in addition to the regular campaign checklist. Do not call the DDD randomly as you will be killed after 2 mistakes. Be careful when letting residents through as well. Ensure you double check as they will kill you immediately if they're a doppelganger.

Haunted
Capture the ghost of the mask.
For this achievement, you'll have to reset the mode till you see a woman with a mask warning you about a mask ghost. However, please note that she can appear at any point in the mode. Once you've seen her, carry on as per usual till you see the mask ghost wearing the mask seen in the achievement icon. Wait a bit but call the DDD before she gets to the middle of the room and you will get the achievement. Do not wait too long to call them as she will instant kill you forcing you to restart.

There are tips below in the General Tips section of this guide that you may find useful for completing this mode.

Landlord
Add a neighbor to your building in Custom Mode
Simply open this game mode and create your own character. The achievement will pop once you're done.

In order to get some of the endings, you'll have to ensure none of the residents die. This section will have some tips to ensure you get the ending you want.
Some anomalies are easier to spot than others, for instance, having an extra eye or having arms around their neck.
It does not matter whether or not the resident is wearing a hat.
General checklist I used for my perfect runs:

• Check their ID for anomalies, the DDD symbol, compare the picture on the ID with the guidebook/ roster, ensure the spelling of their name and identification number matches up and ensure the expiration date and the month on the card, only those after 1955, are correct.
  
• Check the entry pass, compare the DDD symbol and approval stamp, the spelling of their name, the picture on the pass, their apartment number as well as their job if it states it (If their job isn't there, its not an automatic disqualification, some entry passes simply don't contain this information). As for their apartment number, even if it looks correct, make sure the floor and apartment number matches up with the one in the guidebook/ roster.
  
• Check their hair, brows, eyes, ears, nose, mouth, moles, freckles, chins, facial hair and scars, compare these features with the guidebook/ roster. Sometimes the ID and entry pass may match up with their current appearance but if you check the guidebook/ roster, it may show that some features are mismatched. (I find that the moles and lip size are the hardest to spot, so keep a lookout for those. Selenne and Elenois have moles on opposite sides and are otherwise identical.)

The phone is also very useful in these runs:

• If they have a roommate, call them and ask if everyone at home is present. Doppelgangers that aren't on the entry roster sometimes have a perfect ID card and entry pass, you'll have to call their roommate to double check.
  
• Even if they don't have a roommate, you can still call their apartment to check. Sometimes the resident isn't on the entry roster, and when you call their apartment, they pick up. This is how you know that the "resident" in front of you is a doppelganger.
  
• Call the roommate to check if any of their documents are left at home. Sometimes doppelgangers will have both documents despite the roommate confirming that one of the documents were left at home. Either that or the "resident" left a document at home but they're supposed to have both with them.

Doppelgangers cannot pick up the phone, hence:

• In order to double check if you let the right resident in, you can call their apartment after you let them in and see if they pick up, if they don't, it is highly likely that you let in a doppelganger.
  
• Sometimes, you'll see a doppelganger with the right documents and appearance, after you've let the resident in already. The only way to tell if the resident you let in was the right one is to call their apartment and hope they pick up.

If you accidentally let a doppelganger in, you have 2 options:

1. Reset the day, your progress will only be reset to the start of the current day.
   
2. If the resident lives alone, you can choose to leave the doppelganger in there, but when the real resident shows up, turn them away instead so they don't die. This should not invalidate your achievement run.

For further tips, the comments section of this guide also has some great advice for some of the more tricky achievements so you should check that out if you have the time.

Let me know if I need to add or change anything.
Thank you for reading and please give a rating/ award or comment if this guide has helped you!^^