Well that was fun! The hard is pretty hard. Had to beat it on easy first. Overall, it feels very solid. Allowing the player to choose their difficulty as they go is a great idea! I can keep up the pressure if I'm feeling it, or I can hop back over to easy if I need a break. I could see that being a very good mechanic especially in longer levels. I wish there was more to play.
One small critique is that I wish the "dash ready" sound effect was a little 'happier'. The first few times I played it, I thought I was getting hurt after each dash (I thought I wasn't quite dashing all the way over the spikes, for example).
But a great entry. Well done.