Key

Keys are special items found by Luigi in Luigi's Mansion and in it's sequel. They help Luigi unlock doors. Luigi can obtain a key by lighting up a room or doing something specific (for example: the key leading to the Butler's Room is obtained by lighting up all candles in the Fortune-Teller's Room while it's still dark. Special Keys are obtained after defeating a boss Portrait Ghost. Some of them look like symbols found on playing cards. For information about Special Keys, see below:

Special Keys in Luigi's Mansion

 * Key to Area 2 (obtained by Chauncey): The door that leads Luigi to Area 2 is the main one of the lower part of the Foyer. Also, the door has a heart shape on it.
 * Key to Area 3 (obtained by Bogmire): The door that leads him to Area 3 is the one near the Bathroom on the first floor and the Conservatory. It has a club shaped on it.
 * Key to Area 4 (obtained by Boolossus): The door that leads the green-capped plumber to Area 4 is the second door found on the Balcony on the third floor. It has a diamond shaped on it.
 * Key to the Secret Altar, some call it area 5 (obtained by Vincent Van Gore): The door that leads him to King Boo's hideout is located on the basement where Luigi goes through the hallway and reaches the last door. The door has a spade shaped on it. It's also the only Special Key that's not dropped by a boss Portrait Ghost nor leads to a different area.