Skeleton Key

The Skeleton Key, said to be Luigi's favorite item. is a key featured in the first games of the Mario Party series. The item could unlock special gates to provide access to new paths on the gameboard.

In Mario Party 2, it had a bow on it's head, indiacting it was a female. In Mario Party 3, it had big black eyebrows, assuming that it was now a male.

The Skeleton Key stopped appearing after Mario Party 4. The item was replaced by the Mini Mushroom, which allowed partiers to access new paths via Mini Pipes.

Trivia

 * The Skeleton Key is named after an actual kind of key used on some types of locks.