On most levels with the doors you shoot to cause them to open you can use a door to climb up many many walls/levels above. Simply shoot the door and stand with the front 1/2 of Samus wedged where the door will reform. After you are partially ''sealed'' by the door just quickly tap up and down on the control pad. You will slowly climb up the wall. It is possible to get stuck while using this trick.
Invincibility
Enter the password on the password screen.
Effect
Password
Invincibility,Morph Ball, Missles
NARPAS SWORD0 000000 000000
Morph Ball Double Jump
Turn into the Morph Ball, and slide off a platform or any other surface that allows Samus to stand in the air as Morph Ball. While in mid-air, press UP, and Samus will now be standing on her feet without any ground below her (She will be doing this still in mid-air), then quicly press ''A'' to perform an jump from the standing position you were placed. This trick will only work as long as Samus's sprite is stationary, this means that if you hit the D-Pad from you standing position, you will not be able to Morph Ball Double Jump.
Play as Suitless Samus
Beat the game in under 2 hours, and then at the password screen press 'Start'.
Quick end
Any time in the game you need to quit fast press start on Controller one , Then press Up and A on Controller two at the same time.This code will end your game and go to the password screen.
Skip Kraid and Ridley
You have to have gone far enough to get the Ice beam. Now go to the room where the bridge needs to be formed and there's the statues of Ridley and Kraid. Before you enter that room, have the winged enemy chase you and hit you as you are going through the door.
If done correctly, the enemy follows you into the next room. Simply freeze him and use him as a stepping stone to get across the gap - without beating Ridley or Kraid. You can theoretically beat the game in under 20 minutes by using this glitch.
Climb up Walls...