Walkthrough: Once in the main room again, head over to the area with the Save Station and go to the right. Use the Spider Ball and Lightning Armor to get up to the top hallway to find a door that can only be opened with a Wave Beam. Go inside, and start dropping down the tall room to enter the next area. Drop down once more to the shallow waters, bombing the block on the left afterwards. This will lead to the next Energy Recharge Station. Destroy the block on the right most wall to find the next room, and then break through two floors and Bomb the block on the far right.
Falling down once again will get you to another door. Inside said room is where you'll find the High Jump Boots, the same that will let you jump twice as high now. After obtaining them, you need to get back to the main area of Area 2. You can get back there by one of two ways: by using the elevator or by using the Teleportation Statue.
Missile Expansion: In the same room you obtained the High Jump Boots, Bomb the floor in front of the ramp and head left. In the next room, use a missile to destroy the block above, then use the High Jump Boots to reach the next Expansion.
Energy Tank: After breaking through the two sets of floors on your way to the High Jump Boots, find the weak point in the third floor and through it. Reach the bottom and then move through the water, using the Wave Beam to open the door to the next room. Immediately activate your Lightning Armor to get close to the toxic purple gas, and then shoot a missile to the top left corner to create an opening. Run through the gas quickly and climb up to the opening. Drop down to the bottom from here, and then open the door you come to. The Energy Tank will be all the way down the passageway you come to.