Puzzle
Notre-Dame organ puzzle
Get in, then find three sheets
The painting in the Main Hall's Gallery of Eternal Night opens when you use The Artist and Brauner's Paintbrush on it. Inside, three sheets feed the Great Organ. Fugue comes from a ghost in the Great Organ Room. Sonata is the Sealed Scriptorium clue in the Stained Glass Gallery. Concerto is at the top of La Flèche. You do not have to defeat every enemy in the gallery. The Sonata clue is the goal.
On the Great Organ, jump the keys in the printed order. Fugue is circle, sun, circle, Virgo, Leo. Sonata is Sagittarius, Capricorn, Pisces, Aquarius, Capricorn, Sagittarius, Capricorn. Concerto is Gemini, Cancer, Virgo, Leo, Virgo, Leo, Gemini. Each finished line shuts off a beam. Three beams down, and Death is waiting in the Choir.
The fourth melody
IGN describes a hidden fourth melody read from candle counts in the Stained Glass Gallery: ten inputs, counted from the middle toward the right and back to the left. Completing it awards War and Famine and finishes a Works of Mercy step for The Shadow. I do not have a verified symbol diagram for those ten inputs, so I am not drawing one. The candle-count method is the clue. The symbols themselves need a screenshot I do not have.
What I ran into
I could have faked the fourth staff from memory of a thumbnail. I did not. The three published lines are here in full. The fourth is described as a method, and the missing diagram is named as missing.
Questions
How do I enter Notre-Dame?
Use The Artist and Brauner's Paintbrush on the painting in the Gallery of Eternal Night.
What does the fourth melody give?
The War and Famine dual blades, plus progress on The Shadow's Works of Mercy.