/ This is a missable trophy simply because there is nothing in the game itself that requires you to interact with the items involved. /
In the back hallway of the second floor (past the first three rooms) is a room with Nurse Edna and then Big Ed's room. The computer in this room, when you USE it, will have the classic Maniac Mansion game on it. All you have to do is use the computer to get this trophy, but there is another trophy involved with it.