Chapter 4 of Deltarune hides a secret boss that’s easier to access than the **Chapter 3 arcade-based fight** but requires puzzle-solving with sheet music and thorough exploration.

Golden Piano Puzzle

• Find the golden piano room mid-chapter.
• **Three hidden sheet music pages** are required to unlock the boss.
• Missable: Progressing too far (e.g., completing the second sanctuary) can permanently block access to one sheet.

Sheet Music Locations

1. Behind the Waterfall

• Return to the donation box area – the first sheet is hidden behind the waterfall.
• Warning: Unavailable after advancing past the second sanctuary.

2. Shadow Room

• In the dark area where “Jockington grows a beard,” climb the upper-left wall.

3. Tea Room Area

• Near the old man’s study – backtrack to find a concealed side path.

Triggering the Fight

• Play the completed tune on the golden piano to initiate the boss battle.

Boss Strategy

• Not the toughest, but the final phase demands focus.
• Use **Susie’s heal** and **Vampire Axe** for survivability.
• Ignore the Shadow Mantle – it has no effect here.
• Reward: **Shadow Crystal**, consistent with earlier secret bosses.

Note: Rumors suggest earlier choices (e.g., tea scene) may alter the boss’s “shadow version,” but core mechanics remain unchanged.

FAQ

• How many sheet music pages?
  Three: waterfall, shadow room, tea room.
• Can the puzzle be missed?
  Yes – progressing too far locks the waterfall sheet.
• Boss difficulty?
  Final phase is challenging without proper healing or timing.