BS The Legend of Zelda/Quest 2/Dungeon 4

Before dungeon 4
Head north, north, west, north and into the cave. Here you can buy the Blue Ring, if you have 250 Rupees to spare. This halves the damage you receive. You can also buy Meat here, but you don't need that just yet. Go back outside and head east. Step onto the wooden platform to reach Dungeon 4.

Dungeon 4
Head north. Use the Candle the light the room, then kill all the Gels for aKey, then head north. Kill the Keese to get some Bombs. Bomb the eastern face and go through to find aKey, then return. Head north. Light the room and kill the Darknuts for some Bombs. Head east for the Map. Head back west and go north. This room contains a worm miniboss. Simply shoot it from afar with arrows or sword beams. After you kill it another appears. Kill the second one then unlock the door and head north. Grab the Compass. Head north, east, north and kill the enemies for some Bombs. Head west. Kill the Darknuts for aKey and push the left-hand corner of the diamond aside to enter the basement. Grab the Ocarina and go back upstairs.

Head west, kill the enemies, then head south. Light the room, unlock the door and head south. Head south again, through the basement, and into the next room. In here the mouse-like creatures can be destroyed by playing the Ocarina. Head west to fight the boss. First play the Ocarina. This makes the boss break up into smaller eye things. These eyes are weak to bombs, which are easier to kill them with than sword beams or slashes. When they're all dead grab the Heart Container, then head north and grab the  Triforce piece.