Ice beam - Shouldn't unfreeze indestructible enemies with a second shot, just like in Metroid. Screw attack - Should be able to destroy frozen enemies, except indestructible enemies (like bullet bills). Shouldn't be able to destroy indestructible enemies, you should just go through them like in Metroid. Would also like to hear the "indestructible sound" repeatedly when you go through an indestructible enemy, or one that's frozen. That's a minor detail though, and isn't really that important, but it would make it more Metroid like.