Cool game, I like how you hinted the coin secret in the ground, I did had to take a doubletake and then spotted it! I really like the Intro animation, thats a great idea but maybe make it go faster and faster as it goes on so people dont have to skip it.
Maybe you want to think about giving the enemies a Spike on their head to indicate that you cannot jump on them, everyone will try that because of convention and a spike would make it clear that not the way to go.
Also having this play in the browser is a genius play I will have to look into that myself.