Kraid
Hop down and enter the room on the left to save your game. Before exiting the save game room, walk along the wall on the left side. There's a hidden tunnel. You can enter it now with the help of bomb-jumping (otherwise you'd need the hi-jump boots to hop in morph ball form). Go to the corner and bomb-jump while pressing the directional pad against the left wall. Traverse the narrow tunnel and use bombs to destroy any obstructions. Grab the missile tank in the hidden room.
Exit the save game room to the right. Open the red door with a missile and hop over to the right. Leap across the pillars and snag the missile tank. Destroy enemies and blockages with your primary weapon and cross this corridor to the right. Move through the door at the end.
The next room contains a tube on the right side. You can go up the platforms on the left but the ceiling is blocked. Instead, bomb the ground adjacent to the tube's bottom. Roll into the hole and down into a recessed pit. It's another propulsion device. Roll inside and set a bomb. The device propels you upward (destroying those enemies in the process).
At the top, roll to the left and to the first narrow passageway so you can grab the missile tank. If you miss it (or once you've grabbed it), you can use the device again to propel yourself back up the tube.
Use your power grip and jump up the wall using the small corners to grab hold. Keep going to the upper door on the left. In the next tunnel, destroy the blocks on top of the pillar to open a hole through. If you need health or missiles, stay close to the tube in the ground and shoot the enemies that emerge. Exit the tunnel to the far left.
Destroy the blocks in the next tunnel and drop down. There's another propulsion device here. Before you enter through the door on the bottom right, use the device to launch yourself up the left side of the screen. As you descend after the blast, push the directional pad to the right and you'll enter a new passage.
Open the red door on the right side with a missile. Inside you'll find an unusual structure. This device controls the "zip lines" that are scattered throughout Kraid. These zip lines aid in your movement around Kraid. To activate the zip lines, jump into the device and enter morph ball form.
To use the zip lines, shoot the red button on the ceiling to call the line toward Samus. Then jump up and grab hold to transport along the ceiling to the opposite side of the screen. When you do so here, you'll automatically hit an energy tank. Enter the door to the right and save your game.
Exit the save game room to the right. Walk to the edge of this small alcove to drop down in front of a door below. Enter the door on the left. Leap to the room's center and prepare for another boss battle. The creature emerges from the pool below and will attack the left and right platforms--whichever you are currently standing on. You must use the zip line overhead to avoid the attack. When you drop to the other side, use your missiles to hit the creature around its neck. The creature also causes the hazardous pool to rise. Get on the highest platform to avoid taking damage. Repeat the process back and forth until the beast has been destroyed.
Before you exit the room to the left, drop down into the recess (where the creature came from). Hop over the pillars toward the left side. Destroy the block in the upper left corner of the recessed area (using bomb-jump if necessary). Maneuver through the tunnel into a secret room on the other side. Blast the block with your primary weapon and leap to the missile tank.
It's time to exit the area. Return to the previous room and go left. Use the propulsion device to launch to the very top corridor. Proceed to the right and use the zip line to cross. Destroy the blocks behind the pillar and exit to the top right corner of the map. Drop down to the top of the tube then down to the bottom. Enter the door on the left. Retrace your steps through this corridor and enter and use the save room on the left side.
