Weight

The Weight can be found in a chest on the second floor of Boo's Mansion. The chest was guarded by a Boo under the orders of Lady Bow. However, by using the Record, Mario can distract the Boo long enough to get the Weight from the chest.

The Weight is necessary in order to continue through the mansion. By launching off the couch in the lobby and hanging off the chandelier, it reveals a hidden passage. Mario can then attach the Weight to the chandelier in order to keep the hidden passage open for use.