You need to get
-All weapons
-All helmets
-All Armors
-All Scarves
-All Rings
-All Accessories
-All materials from monsters/chests
-All items
-All food meals prepared
-All Bullets
Weapon list is broken down here
https://gamewith.net/bloodstained-ritual-of-the-night/articl...There are a few hidden treasures located in the Twin Dragon tower that won't appear on your breakable wall detector as they are in open, yet hidden, chests. Also where you fight
there will be a hidden tiara on the left side of the chips, its obscured purposely.
Also be aware each of the secret bosses carries a special material
Your best way is to get 1 and keep dismantling, then using that material over and over.