Start playing the game as normal.

During the Hide-And-Seek game look at Ib’s fallen painting

Right after meeting Garry, try to read the name of the rightmost painting [Garry’ chat meter 1/9]

Backtrack to the room with the walking stool and interact with it [Garry’ chat meter = 2/9]

Go back even more and interact with the ant [Garry’s chat meter 3/9]
After this you can continue with the story normally.

Look at the porcu-puss painting with Garry after it's in there [Garry’s chat meter 4/9]

Save your game, and make a new save [SAVE B] before entering that room.
Load the first save [SAVE A]

Don’t kick the head. [Friendship meter =2] [Death meter = 0].

Choose to go around the statues [Death meter = 0]
Note: If you happen to go through the hanged-man painting while running away choose not to take the shortcut.

Puck up Garry’s coat and then talk to him [Friendship meter =4]
Talk with Garry again until he starts repeating the same dialogues over and over again

Pick up your rose and talk with Garry again until you see all his new dialogs [Garry’s chat meter 5/9]

Interact with the milk puzzle [Garry’s chat meter 6/9]
After you enter a certain room and the light go off pick first or second option. [Friendship meter =5]

Pull only the 4th string from the left [Death meter = 0]

Don’t pick the first option [Death meter = 0]

Don’t kick the doll [Death meter = 0]

Check the M page

*If you’re confident that you chatted enough with Garry and saw at least 20 different dialogues go ahead and escape the doll room, otherwise let Garry fail. I recommend you save Garry just to be sure you have enough friendship points.

*If failed to escape the doll room [Death meter = 2]

*Save Garry [Friendship meter =8]

Choose treasure and interact with the diamond [Garry’s chat meter 7/9]
Choose “Look at the pudding” and “Talk with Garry” [Garry’s chat meter 9/9] [Friendship meter =9]

Pick option 1 or 2

Make a new save [SAVE C] before progressing.
LOAD SAVE C

Give your handkerchief to Garry

Make a new save which will serve to see the true ending [SAVE: TRUE ENDING]. Don’t save again after this so you can see 2 endings with this save.
*If you are in New Game+ you can explore the secret area below, otherwise you can visit it during your next runs.

Use the save you just created (the true ending one) to see both endings:
Go with mother [Normal Ending – Ib All Alone]
Take Garry’s hand [True Ending - Promise of Reunion]

LOAD SAVE C
Don’t give Garry the handkerchief

Take Garry’s hand [Ending - Memory's Crannies]

LOAD SAVE B
Close your eyes and let Garry kick the head. [Death meter = 1]

Choose to take a shortcut [Death meter = 2]

Go through the hanged-man painting while running away and choose to take the shortcut. [Death meter = 3]

Pull the third string first before pulling the right one. [Death meter = 4]

Save and create a new save [SAVE D] before moving forward.
LOAD SAVE B

Choose first option “I’d leave with Garry”. [Death meter = 5]

Kick the doll [Death meter = 6]

Fail the doll room [Death meter = 8]

Choose “Garry…?” [Ending: A Painting's Demise]

LOAD SAVE D
Choose second option “I’d leave with you, Mary”. [Death meter = 4]

Kick the doll [Death meter = 5]

Create a new save [SAVE E] before entering the doll room.

LOAD SAVE D
Fail the doll room [Death meter = 7]

Choose “Garry…?” [Ending: Welcome to the world of Guertena]

LOAD SAVE E
Escape the doll room [Death meter = 5]

Save after taking Garry’s lighter (or before taking it if you want to see the two dialog variants of the last ending, but grab the lighter for this ending anyway).
*Note: Don’t save again so you can use this save to see the next two endings

Burn Mary’s Portrait and then leave for the real world [Ending: Forgotten Portrait]
LOAD SAVE E
Leave and go to the real world without burning Mary’s portrait [Ending: Together, Forever]
*If you saved before taking Garry’s lighter you get two small dialog variants right at the very end of this ending depending of if you’re carrying Garry’s candy or lighter.

Here are my save files for each ending as described in this guide.
The zip file contains All Endings + True Exhibit Gallery 100%
https://drive.google.com/file/d/12c8ZOjetE6_4JXXGsFBYSkV6BEdxRPjP/view?usp=drive_link

I'm too lazy to publish guides but this game has earned a special place in my heart since I played the original version years ago and I want everyone to see those sweet ending cards without ruining their exploring experience with spoilers.