This is my strategy (might not be in order and glitches may have to be preformed) There are extra Skullettes just in case you mess up one or two.

You need 13 Skullettes from the first area to open the door to the second area which is the second and third image

And 31 Skullettes to open the last door (not shown) to the maze and defeating whisp. Hope this helps, I’ll ad some videos explaining when I can!

Not playing the game, I was wondering why you needed some of the collectibles

To unlock 2 areas