Spectral Bones

[FiveFour]

In the least spoiler-y way possible, could someone tell me how many bones there are/ what to do with them when I have them all?

[Drox]

https://steamcommunity.com/sharedfiles/filedetails/?id=3353374583&searchtext=bone

[zero]

5 to dig up, and a 6th spot to find to do something with them.

cannot be more vague then that