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