This is a really excellent game. Loved the mechanics / abilities, the animations, and the level design. The controls were also really good (even though the jump is a bit floaty, it didn't feel like it detracted from the experience at all).
I really don't have much else to say, so I'll nitpick some small things that I would have liked to see:
- The fact that I collected the bones with no apparent use was a bit of a bummer, but presumably that's partially due to time constraints.
- The fact that checkpoints only healed you when you activated them (i.e. only if you have another one active and then come stand on it) was a bit annoying. It seems to encourage you to do a checkpoint run where you go to a different area's checkpoint, only to come back to the previous one, which is just busywork, really. Or to just avoid activating the checkpoint because you might want to heal later. Both of these don't seem like the kinds of things you'd want to encourage.
Anyway, this is a really excellent game; amazing work!