This isn't really too bad, just very time consuming...I recommend playing the levels on normal, then hard, back to back. This way it will ensure you have the level fresh in your mind for hard, instead of coming back later and having to relearn the level layout. No one particular level gave me too much trouble on hard, however, the final boss on the third checkpoint can be somewhat overwhelming. Really, the only tip I can give, is when jumping, keep your shield up. Blocks start coming rapidly, so it's best to just always have your shield up when you jump. This is an awesome game and I hope everyone has as much fun with it as I did!