How do you kill the piano ghost?

First, you have to bang on each of the instruments to get them to play the Mario theme. Then, go walk over to the piano seat. A girl ghost will appear and play a song on the piano. Then, she will either ask if you know what the songwriter was thinking of when he was writing that song or ask what game the song was featured in. I think the song was supposed to be about water and was featured in Super Mario Bros. 3. If you guess wrong, just walk outside and start the process over. If you get it right, she'll start to use music sheets to attack you, when this happens, suck them up. When you do, she'll be vulnerable to the flashlight beam. Flash the beam in her face and suck her up.

Walk up to all the instruments and interact with each one so they start playing music. Then go over to the grand piano and talk to her to guess the song she is playing. Once she starts to throw sheet music at you, vacuum them all up and she will be vulnerable.