The Donor's Despair is a song from the Shovel Knight soundtrack. This song is the theme of the Hall of Champions stage.
Music Sheet #14 can be found in Hall of Champions, Room 5a. In the top left room of the Hall of Champions is a Music Sheet you can get to by jumping over invisible gaps in the floor.
A bit foreboding for a peaceful, non-threatening portrait gallery, don't you think?
- "Bard: Let's see here... Oh, you found "The Donor's Despair"! "Make it spooky," they said. I don't understand, it's an art gallery! Why spooky?"