one of the items/weapons you can unlock is the Alchemy Flute.
once you have the flute and sheet music(which can be found in various locations) you can learn new songs from Rojas, playing the right song in the right place can unlock hidden areas/move walls/etc.
like all things in VonGarland Castle these extras will help you complete the game more easily, but are not required. The game can always be played like a classic mega man or Castlevania, meaning you can just beat each level and boss in order to beat the game. but there are loads of extras for anyone who is willing to take the time to find them :)
as always thanks for reading!
if you know folks you think might enjoy the game feel free to tell them to give it a wishlist and follow :)
-Ash
Monster Robot Studios
-Games for Humans-