Zelda 3 A Link to the Past Walkthrough on Super NES: The Swamp Palace, 2nd Crystal (GBA, SNES, Super Nintendo)

Swim to the left and kill all the enemies. Open the chest and go through the door. Make a hole on the left and take the palace map. Go back out, lift the bottom skull (1) and take the key to open the bottom door. Cross through, take the stairs and the door opposite. Lift the skull to find the key. Go back out, and take the door at the top of the stairs. Hit the heads with the hammer and push the lever to the left (2). Go back out, fall into the water and take the stairs then the door on the left. In the large room, take the bottom door first. Go around to the right to push the stone and get the compass (3).

Go back into the central room and take the door at the bottom left. Cross through, take the stairs and take the door opposite. Lift the skull to get a key (1). Go back into the central room and take the door above. Hit the sphere (2) and push the lever. Hit the sphere again and go back through the bottom door (via the central room) and take the door on the left. Go down the stairs, push the bottom block to the left and the middle one upwards (3). Take the door at the top.

Cross the room, push the block at the top right and fall into the hole (1). If you hit the sphere correctly, you can go to the right and take the big key. Return to the central room and open the large chest. You get the hookshot. Use it on the right (2) and lift the skulls to get a small key. Return above the chest and use your hookshot upwards (3).

Take the door, go to the left and lift the top skull. Push the statue onto the button (1) and go take the door on the right (not the stairs). Take the stairs and push the lever. Go down the small stairs and take the door on the left. Take the door at the top then take the hidden door under the 2nd waterfall from the right (2). Go up the stairs and take the door at the bottom. Swim to the right and take the key under the skull (3). Then swim to the left and open the door. It's the Boss.

To kill it, use the hookshot to grab the small creatures and kill them one by one with your sword. The giant jellyfish gets angry and flies away. Charge your sword and wait for it. Be careful, it will try to fall on you. Avoid it and release your charge to defeat it.

You can now continue the adventure by searching for the other crystals whose locations you now know. Here is a save file for the ZSNES emulator (to be copy-pasted into the Rom folder).