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