Mad Piano

The Mad Piano is an enemy appearing in Super Mario 64 and Super Mario 64 DS. It is a monstrous animate piano that follows the playable character around when approached.

Super Mario 64 / Super Mario 64 DS
The Mad Piano looks normal at first, but when the player approaches the instrument, it begins to open and close its lid, revealing sharp teeth. The Mad Piano proceeds to chase and attack the player (while making the sounds that sound like someone hitting its keys) until they are far enough away. The Mad Piano appears only in Big Boo's Haunt and protects a Red Coin found behind it. If hit by the Mad Piano, the player loses three wedges of health.

It is impossible to defeat this enemy in any way, despite the Nintendo Power Player's Guide erroneously stating otherwise.

Mario Party 2
A similar piano makes a cameo appearance in Mario Party 2 in Horror Land at night, where it plays in a band with a violin and trumpet.

Mario Party 8
Another similar piano appears in Mario Party 8 in the board King Boo's Haunted Hideaway.

Luigi's Mansion 3
What appears to be the Mad Piano makes a cameo on a poster in the hotel The Last Resort in Luigi's Mansion 3. Amadeus Wolfgeist, the boss of The Great Stage, possesses his grand piano to attack Luigi in a similar manner.