Amazing game, but the medals are broken
There seems to be a problem with the medals unlocking. For some reason only the Line IX medal, the Welcome Home medal, the Return to Me medal, and the Perpetiel's Wings medal unlocked even though I met the requirements for all of the medals (except maybe the Loki medal, do you have to kill all of the soulstealers for this medal, or just the enemies in the living world? If you have to kill the soulstealers I'm not sure how to get the medal, the only way I found to kill them is to drag them into the living world.). I wouldn't normally mention this, but you have to unlock the medals to see the story.
Other than that this game is great, and easily the best platformer I have played on Newgrounds in months. The puzzles were challenging, but not to the point of outright frustrating, and all of the jumps are possible to make (even if some are difficult, mostly the ones where you have to jump between the living and dead worlds). The music in this game seems to fit the mood perfectly, and the controls are good (now anyway, I saw a lot of complaints before you updated it). There is a small amount of story to give you an idea of why you are doing this, but a small enough amount to let people decide on the meaning for themselves (not something I am normally a fan of, but it really works here).
The only thing I would even consider changing (besides the medals not working, but I'm not sure if that is something from you or something from Newgrounds) about the game is to add a 2nd ending for level 11 (one in the opposite direction), since I think that would fit the mood of that level. That is just me though, some people would likely dislike that.