How do you beat the nightmare?

When you enter Nightmare's room, start Space Jumping at the top left part of the room. When Nightmare emerges, fall to the bottom of the room and stand underneath it, where you will shoot missles upward. There is a strange thing in the center of the NM-X (Nightmare X) that you have to shoot, so fire missles once you are centered under the thing. After a few shots, The thing you were shooting will begin to turn, making the gravity more powerful. Give all the suicidal attempts needed to keep shooting the thing, even if you are knocked out of the way. When NM-X flys high above you, your Missles will be pulled down by the gravity, so now you gotta fully charge your beam and shoot. Keep repeating as neccesary until the whole thing starts to flash, where you will need to latch onto the ladder on the left side of the wall and shoot Missles at it's face . If it gets really close, Space Jump away. This is the toughest part. NM-X goes about the room until you latch onto the ladder again, but only if it is in front of you. Hopefully you are positioned so you can shoot the face again. Keep doing this until a Core-X emerges. You know what to do. In the end you get the Gravity Suit. To escape after the battle, go to the right side of NM-X's room and blast the hatch while running out, starting your Speed Booster and blasting through the wall.

When you drop down, get onto the top of the ladder and wait until it gets level with you, then drop down and fire a missle diagonally.

If you timed it right, it'll hit the spinning canister and do damage. Wait until it comes down and hop back onto the ladder and repeat the whole process until it starts to bend gravity, then you have to use charged shots. When the canister finally starts flashing nonstop, get back on the ladder and wait until the mask blows up to reveal the hideous thing underneath.

Now you have to hit the face. Stay on the ladder until it gets too close, then go over behind it and wait until it realizes that you're not there, then space jump around it as it floats around. Get back on the ladder when it slows down and start firing at the face again. Repeat the process until it becomes a core-x. Then you know what to do.