Tree trunks are looking nice, though I worry about a their full range of lights/darks, being BG tiles. Readability problems easily arise. You have the right idea with the blue mountains BG. Though, when in-game everything is moving around so it becomes easier to distinguish depth correctly.
I don't like the tree canvas however - it's too mushy and cloudy, pillowy.
When you look at successful protagonists in games, they usually have unique features. Things that imply some sort of backstory perhaps - a strange haircut, some weird item, an outfit with some flair. Your little guy just looks like some random extra from SpongeBob Squarepants.
I also wonder about your use of black outlines - how you use them in some places, but not others. Feels inconsistent. I'd try adding outines to your foreground tiles, see what happens.
On a sidenote, if you're really going to complete this game, are these gfx all you've done? If you're creating polished art, you should have a complete design doc outlined and established. Do you have that?