I tend to dislike games that mix the pixel-art with another artstyle (in COIN the background is probably vector, and the water not pixel too), but the colors are cohesive and the contrast is great.
There's a reason for that... in the first half of this TIGS competition, artists made only game assets like sprites and backgrounds and music and such. The second half of the competition was for game programmers to then pick and choose out of all of those assets and make a game out of them. The rule was that you couldn't change the assets at all, you had to use them as is. There's a lot of mixed art styles in the compo entries
Downloading now...
Edit:
Nice . I just played through to the boss, but I got game over. It's strange how challenging a game can be with just two kinds of enemies and a couple of pits. Whenever I'm designing a game I'm always thinking "well, I have to have several kinds of enemies or players will get bored," but it's not really true... you use the two you have really well. The level design is really good, I think that has a lot to do with it. And you did a nice job incorporating different assets... it feels pretty complete.
I did have an issue with the tree branch platforms, though. I could never tell where they ended so I fell a lot. And I came across a weird bug once where a coin wouldn't disappear no matter what... I ran over it several times and it just stayed there on the screen, but it appeared to be a one-time deal. My only other real complaint is that the game closes when you lose your last life... a Game Over screen and the option to continue would have been nice. Oh, and the boss should have had a pattern to his fireballs instead of them being random.
Anyway, it's really nice work . I've only played a few entries so far but you have my vote for sure.