also worth noting that you get a bonus for playing on higher difficulties vs playing on easy mode, so the harder the game the more rewarding that bonus. also on hard mode all the invincibility coins are only going to be a health restore and more gems are around instead of health restores
a big tip here is as of this post for the US version anyway its at patch 1.1 and with the new patch it does some new and for the better fixes in the game
1) for those who don't like the cutscenes they have an option to turn of 95% of them
2)the pogo cane works so much better making the game almost too easy now my first run on extreme I was on my last hit and life, just played it for a friend and did the game on extreme in only 1 life and only got hit when I was being silly.