I really like this a lot. The music, art and animation work really well together and running through the world and making attacks feels pretty solid. I really think this is a game that could be polished up into something really nice. A couple small pieces of feedback: I would rather not have coins that are impossible to get (i.e. inside things that will kill me). I also feel like the grass with spikes in it is a little too hard to spot, I would rather have things that can kill me be obvious. The same goes for your friends, which you have no way of knowing are your friends except through trial and error. I think it would be best if the player could jump into the game and be able to read the world without being taught to understand what will happen to him if he runs into something.
These are small things but they were a barrier for me getting into the game that I had to get past before I could start enjoying it, which not everyone will take the time to do. That said, once I figured these things out I did really start enjoying the game and played it for a while. Really great submission altogether, good work!