I've been working on a personal project called "The Precipice" on and off in my spare time (which is dwindling more and more these days...)
In the beginning I set out to create 1 character, 1 creature, and one environment to set the mood for what I hope will one day grow into something much, much larger.
These were the initial thumbnails and anatomical explorations for the first demonic creature in "The Precipice," A fallen Harpy. I didn't plan to concept a harpy in the beginning (as you can see from the thumbnails) But it started to develop that way over the course of the ideation.
I also sketched out the flesh, bone, and muscled groups separately but it looked much more appealing when compiled together for that DaVinci-like look.