The difference in modes is as follows:

ZGDNWtQDH - Normal Mode: The game as I made it.

ZGDNWtQDH-EM - Easy Mode: The game as I made it, but you start with 5 hearts, and the heart pieces are now heart containers.

ZGDNWtQDH-HM - Hard Mode: The full heart containers are back, and beleive me, you're going to need them, because the enemies have all been kicked up several notches from last time, making it worthy of it's name. No gold ring in this mode, either.