Red Diamonds (also known as Bronze Diamonds by some fans, despite the fact that it's not bronze) are non-valuable treasures found by Luigi in Luigi's Mansion; this because they are not worth as much as the Gold Diamonds or the Silver Diamonds. Surprisingly, each Red Diamond is worth the same amount as a Coin, tying them both as the least valuable treasures in the whole game. The first one can be obtained by Luigi in the Balcony; to get it, the player must get a Water Elemental Ghost and water all the plants on the Balcony. One of the plants hold the diamond.
King Boo's Crown
King Boo's Crown is the second Red Diamond that appeared in the game, obtained after defeating King Boo after Luigi's tiring battle on the roof. If the player wants to get an H rank (which is the worst and hardest rank to get), he/she must complete the game without collecting any money except for the crown, or at least less than 5000G.