When it gets hard? I went from level 1 to 50, just going to the right of the screen and keeping the "down" key pressed. Just made Power Up upgrades, since no one did any damage to me.
Nice game. Just allow us to change cristals - it's sad when you make a mistake and can't change. Also, you could show the entire combination tree since you can just lose a game and experiment all combinations.
Very Easy... I just used the Wall to protect me or summoned Skeletons... And the final boss, just keep going near him, and when he tries to attack just dodge and go back...