Awesome game.
So far, I'm progressing pretty fairly, however this is not recommended for laptop players. Use a mouse if you can, it helps a lot. There is a trick to getting around Phantas, I'm learning it the way I can. What you should do is when you pick up the key, avoid him by moving forward and by that time, the koopa should have already shot, allowing you to hit him. By that time, he will jump, but while avoiding him, stay towards the right side of the screen, giving Phantas less opportunity to home in on you. Be careful though, after the third jump, Koopa will shoot again. Hope this helps!