If you want good mobile performance, you should change the limits of objects as max. 50, small count of collision per ticks and change low resolution canvas, it would look nice for retro games.
There a third party plugin you can determine the corners for tiles. Don't you allow plugins?
About replay ability, do you want a ghost like super meat boy or just traditional replay with controls such as play, pause, 2x speed, end?
I would like to work with that, but I'm still busy... however pm me how much you would pay me. I will consider it's fine, I will work.