Mr. Passion is a boss from Mother 3. Duster confronts this ghostly composer alone during Chapter 2 in Osohe Castle before he recovers the Noble Spittoon. He is seen blocking a room's door, because he is "performing" Family Matters: 2nd Movement. Really, though, he is making music out of moving furniture and other objects. In Chapter 5, Mr. Passion reappears as an optional boss, only if the characters return to Osohe Castle. This time, he is called Lord Passion and has a new hairstyle, and a new song to perform, Ode to Ancestors: 8th movement.
Both of the songs mentioned by Mr. Passion are the names of his battle themes, in the two respective moments. Fitting his persona, the songs are medleys of classical music, with the first song additionally containing a segment from Etude for Ghosts, the Artsy Ghost's battle theme.