The Final Boss: Metroid Prime:

Their are two phases to defeating Metroid Prime. To get to Metroid Prime, first you have to climb to the top of impact crater. Once you're in the top room, Metroid Prime is resting their. To defeat him you must look at the color of its body. If it is yellow, take out your power beam. If it is purple, take out your wave beam. If it is white, take out your Ice beam. If it is red, take out your red beam. Metroid Prime usually starts out with a yellow body, so take out your power beam. Just keep shooting it. The way it will attack you is it will shoot missels, (dodge them by moving to the side and pressing b), a beam, (move to the side to dodge the beam), giant round energy bombs, (shoot at those with any beam) or it will charge at you,)quickly turn into a morph ball and stay out of the middle lane). As you get its life down it will throw things at you more often and change body color constantly. Finally you get its life down and you think you won but you didnt. Go forward into the giant hole.
(Phase two). Now you have to fight Metroid Prime again except in a form that looks similar to a squid. To defeat it, you have to stay away from it. When it charges up a wave, double jump over it. Just keep dodging those. Then it will lay phazon on the ground and turn invisable. Turn on your x-ray visor and run into the phazon. Lock onto the Metroid Prime, and hold A. Now keep on that same visor or change it into the combat or thermal visor. Now its going to do the wave attack again a few times. After its done it will put more phazon on the ground, but this time also summon some metroids. Shoot the metroids, and put your x-ray visor on again. Stand in the phazon and hold A.

(Tips) The more you hurt Metroid Prime, the more Metroids it sends out. Sometimes to see Metroid Prime when you have to attack it, you have to use the thermal visor. Keep repeating this until Metroid Prime dies. If you defeat Metroid Prime, you can unlock hard mode.