This looks really nice. How you made the cave like a frame really did this piece wonders. The addition of details, such as the firefly(or firefly like) lights, the purple eye'd monster, just breath life into this.
The little minor details are also very well done, such as the grass, the fog, and lighting is very nicely done.
Have no Idea why this is rated M, but hey, I guess it don't matter.
Overall, a very nice piece that gives off a feeling of finding yourself somewhere new.
I like it.