Here is the full list of all 20 The Guest achievements.
Be thankful twice.
Get to the end.
Write BENEFACTOR on the typing machine.
Get into the secret room.
Listen to some music on the record player.
Locate the Team Gotham's headquarter.
Read all the newspapers.
Enter the toolbox password without combining the notes.
Collect all possible objects.
Type the password in the computer.
Complete the dream maze scene withouth failing.
Turn off all the lights.
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.
Complete the valves puzzle in less than 20 movements.
Try consuming the bath pills again.
Call every single number on the phonebook.
Solve the batteries puzzle in just 2 movements.