Exhaustion
Finish Level 1 (Chapter 1 : The Tower Cells)


Hide and seek
Win "Hide and seek" (Chapter 2 : The Innocent Abandoned)

The kids are located in:

• Derek - Church
  
• Eileen - Tree beside the town hall
  
• Marcus - Under the bed in the huouse across the bridge
  
• Lumpy - Barrel near fishing shop
  
• Dennis - Schoolhouse (use the crowbar)
  
• Carol - Cemetery (dig using the shovel)

Fever
Finish Level 2 (Chapter 2 : The Innocent Abandoned)


Headache
Finish Level 3 (Chapter 3 : The Courtyard and Chapel)


Migraine
Finish Level 4 (Chapter 4 : The Circus of Fools)


Vertigo
Finish Level 5 (Chapter 4 : The Cave)


Blackout
Finish Level 6 (Chapter 4 : The Mansion)


Redemption
Find the sentence (Chapter 5 : The Laboratory)

Solves the hidden message in the blackboards. The answer is:
YOUTH HIDES THE KEY TO SALVATION


Hallucination
Finish Level 7 (Chapter 5 : The Laboratory)


Major Depression
Finish Level 8 (Chapter 6 : The Hive)


Behavior Disorder
Finish Level 9 (Chapter 7 : The Morgue and Cemetery)


From life to death
Sort them (Chapter 8 : The Lost Village)

You must able to answer the Chief when he asked you to sort the deceased warrior from the youngest to the oldest. The order is:
Xilonen -> Ometoch -> Tepictoc -> Centeotl -> Huitzilop -> Mixcoatl


Senility
Finish Level 10 (Chapter 8 : The Lost Village)


Schizophrenia
Finish Level 11 (Chapter 8 : The Maze)


Madness
Finish level 12 (Chapter 9 : The Gauntlet)


Insanity
Finish level 13 (Chapter 9 : Morgan's Last Game)

Limbo
Find the children in the wood (Chapter 2 : The Innocent Abandoned)

The children are hidden in the wood near the lemonade stand. You should be able to hear their singing the closer you are to them.



Dance, dance crazy
Make dancing three friends (Chapter 3 : The Courtyard and Chapel)

Play all the three records in the Dr. Morgan's office (Rockabilly Swing Thing, The Ballad of Captain D!ck, Belladonna in A Flat) and watch each three different patients reaction.


Remember you
Play the good melody for the first time (Chapter 6 : The Hive)

You must be able to solve the melody puzzle in The Hive on your first try. Save before proceed to solve it. The correct order is:
Left -> Right -> Right -> Down Left -> Up -> Down Right
(Thanks g000nie for the correction)


You are not alone
Speak with everyone

This shouldn't be a problem if you make sure you don't miss anyone in each chapter. You'll unlock the achievement in Chapter 8 : The Lost Village.

In case you missed those missable achievements, here are my saves for those chapters. I'm not sure this is 100% working so please backup your saves before proceed. Saves are located in
<Steam folder>\userdata\<your ID>\284050\remote\EN
Just drag and drop the saves you downloaded into that folder.

Chapter 2 (Limbo)
https://drive.google.com/file/d/1wLAAig8LClEx6UY3uRTAUbysTkry9uN5/view
This save occupies slot 14

Chapter 3 (Dance, dance crazy)
Unfortunately I have no save for this chapter, I'll update this guide once I replay it.

Chapter 6 (Remember you)
https://drive.google.com/file/d/18fBg8w4y7HMUXgoazjxBqIj1QKl04hAk/view
This save occupies slot 20

That's it for this guide. Hope you'll be able to 100% the game and enjoy it at the same time. May the blessing of Mother be upon you.