Here is the full list of all 20 The Guest achievements.
Use the sign and don't be disturbed.
Call every single number on the phonebook.
Listen to some music on the record player.
Solve the batteries puzzle in just 2 movements.
Turn off all the lights.
Try consuming the bath pills again.
Enter the toolbox password without combining the notes.
Get to the end.
Collect all possible objects.
Type the password in the computer.
Complete the dream maze scene withouth failing.
Read all the newspapers.
Complete the music puzzle without failing.
Try lighting a cigarette.
Wait 8 hours and hit the button again.
Get into the secret room.
Complete the valves puzzle in less than 20 movements.
Write BENEFACTOR on the typing machine.
Locate the Team Gotham's headquarter.
Be thankful twice.