I'm glad you picked up on the Metroidvania elements! The original concept for this was something inspired by Castlevania II, but of course that was an overscope so I had to pivot last minute and use the systems I had to still make something complete (╥ᆺ╥；)
The first idea was that collections were turned into NPCs and more traditional power-ups unlocked new area, but both weren't ready in time. It's still something I'd like to flesh out in the future though!