Here is the full list of all 20 The Guest achievements.
Turn off all the lights.
Listen to some music on the record player.
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.
Use the sign and don't be disturbed.
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.
Call every single number on the phonebook.
Write BENEFACTOR on the typing machine.
Locate the Team Gotham's headquarter.
Be thankful twice.
Solve the batteries puzzle in just 2 movements.