Try to experience the game by yourself before reading the instructions or watching the footage linked in this guide.

In :THE LONGING: endings are meant to be permanent and will require restarting the game or messing with save data to continue playing. Make sure that you have accomplished everything you want to do before committing to an ending.

How to recognize if you are about to reach an ending (non-spoiler versions):

Ending 1:If you are being questioned thoroughly before taking a leap of faith
Endings 2 and 3:If you are about to follow your dreams
Ending 4:If you have patiently followed orders

How to recognize if you are about to reach an ending (spoiler versions):

Ending 1:If you are jumping into a dark abyss
Endings 2 and 3:If you are getting into a bucket
Endings 4If the countdown has ended.

How did you get every ending so fast?

After finishing the game properly I edited stuff to document the other endings and find secrets. I won't share how to edit stuff.

An easy way out.

Name: Suicide
Type of ending: Bad
Video: https://youtu.be/HIK-Uy5f5Jg
Hint 1:
To reach this ending you will have to explore the upper parts of the kingdom
Hint 2:
You will make a small friend before reaching it
Hint 3:
You will need a medium sized object under the ledge to climb it
Hint 4:
Understanding mushrooms will help you overcome the obstacle
Hint 5:
Find a place where there are both green and purple mushrooms
Hint 6:
Don't be scared if you can't see, just keep pushing
Hint 7:
Be confident on your decision

Instructions:
To reach this ending you will need a mattock.
From the map room continue upwards into the caves, opening the caves will take 2 hours.
Once you are on the caves continue exploring upwards.
Find and interact with the spider when there is nowhere to go, it will take 2 days until the web is complete.
Keep exploring upwards with the help of your mattock until you find a tall ledge.
To climb the ledge you will need to grow a mutant mushroom, plant a purple mushroom right under the ledge and then plant a green mushroom on the closest available spot to the left of the purple mushroom you just planted.
Once the mutant mushroom has grown just keep walking to the right.
[Optional] Bring a purple mushroom to light the way.
Once you are at the border of the abyss answer "yes" to the questions.

A dream come true.

Name: Upper World
Type of ending: Mostly good
Video: https://youtu.be/dDK5rooa0C8
Hint 1:
To reach this ending you will have to explore the upper parts of the kingdom
Hint 2:
You will make a small friend before reaching it
Hint 3:
You will need a medium sized object under the ledge to climb it
Hint 4:
Understanding mushrooms will help you overcome the obstacle
Hint 5:
Find a place where there are both green and purple mushrooms
Hint 6:
Bring a light with you to find the way up
Hint 7:
Once the darkness wraps everything and nightmares become real stay calm
Hint 8:
Remember what the face told you about the darkness
Hint 9:
The monster can only see one part of your body, cover it
Hint 10:
Keep walking for a long time
Hint 11:
Once you reach the end you will need to be patient and remember your dreams
Hint 12:
Find another possible exit nearby since the rocks block the normal path
Hint 13:
Remember what the face told you about the young and the old. IMPORTANT
Hint 14:
Stay near the surface to spot the correct person and then rush to the proper place

Instructions:
To reach this ending you will need a mattock.
From the map room continue upwards into the caves, opening the caves will take 2 hours.
Once you are on the caves continue exploring upwards.
Find and interact with the spider when there is nowhere to go, it will take 2 days until the web is complete.
Keep exploring upwards with the help of your mattock until you find a tall ledge.
To climb the ledge you will need to grow a mutant mushroom, plant a purple mushroom right under the ledge and then plant a green mushroom on the closest available spot to the left of the purple mushroom you just planted.
Once the mutant mushroom has grown just keep walking to the right.
[Optional] Bring a purple mushroom to light the way.
Once you find and abyss take the stairs up and to the left.
The darkness will grow stronger until a second set of eyes appear.
Don't get close or you will be sent back home, close your eyes and then walk past the creature without double clicking.
If you don't know how to close your eyes check other guides on "The Darkness" achievement.
Keep walking left until you reach an area right under the surface.
Wait next to the blocked exit during daytime (the first 12 hours of the day, from 23:59 to 11:59) until the old blind man walks towards the well, DON'T FOLLOW THE TROLL CHILD.
Rush towards the well and when the bucket drops to pick up water get into it.

A dream turned into a nightmare.

Name: Tragedy
Type of ending: Bad
Video: https://youtu.be/wJQNvcL3sKU
Hint 1:
To reach this ending you will have to explore the upper parts of the kingdom
Hint 2:
You will make a small friend before reaching it
Hint 3:
You will need a medium sized object under the ledge to climb it
Hint 4:
Understanding mushrooms will help you overcome the obstacle
Hint 5:
Find a place where there are both green and purple mushrooms
Hint 6:
Bring a light with you to find the way up
Hint 7:
Once the darkness wraps everything and nightmares become real stay calm
Hint 8:
Remember what the face told you about the darkness
Hint 9:
The monster can only see one part of your body, cover it
Hint 10:
Keep walking for a long time
Hint 11:
Once you reach the end you will need to be patient and remember your dreams
Hint 12:
Find another possible exit nearby since the rocks block the normal path
Hint 13:
[IMPORTANT] Remember what the face told you about the young and the old. BUT DON'T FOLLOW IT'S ADVICE
Hint 14:
Stay near the surface to spot the correct person and then rush to the proper place

Instructions:
To reach this ending you will need a mattock.
From the map room continue upwards into the caves, opening the caves will take 2 hours.
Once you are on the caves continue exploring upwards.
Find and interact with the spider when there is nowhere to go, it will take 2 days until the web is complete.
Keep exploring upwards with the help of your mattock until you find a tall ledge.
To climb the ledge you will need to grow a mutant mushroom, plant a purple mushroom right under the ledge and then plant a green mushroom on the closest available spot to the left of the purple mushroom you just planted.
Once the mutant mushroom has grown just keep walking to the right.
[Optional] Bring a purple mushroom to light the way.
Once you find and abyss take the stairs up and to the left.
The darkness will grow stronger until a second set of eyes appear.
Don't get close or you will be sent back home, close your eyes and then walk past the creature without double clicking.
If you don't know how to close your eyes check other guides on "The Darkness" achievement.
Keep walking left until you reach an area right under the surface.
Wait next to the blocked exit during daytime (the first 12 hours of the day, from 23:59 to 11:59) until the troll child walks towards the well, DON'T FOLLOW THE BLIND OLD MAN.
Rush towards the well and when the bucket drops to pick up water get into it.

A patient wait.

Name: King
Type of ending: Good?
Video: https://youtu.be/Ze8QZshpxrA
Hint 1:
To reach this ending you will have to follow orders
Hint 2:
And be patient
Hint 3:
You don't need to do much at all
Hint 4:
You will know when the time is up

Instructions:
To reach this ending you don't need anything.
Just patiently wait until the 400 days countdown is over and wake up the king.
You can speed up the wait by making the Shade's cave more comfortable, reading, playing music or sleeping.