The Genie is the boss at the end of the Bottle Grotto dungeon.
If you're looking for more assistance, our Zelda: Link's Awakening walkthrough can help.
Genie boss strategy explained
The Genie boss fight comes in two phases. The first sees the Genie through fireballs at you. Though they cannot be blocked with your shield, these can be dodged easily enough by running side-to-side, which will see them land behind you provided you keep on moving.
After that, it will retreat into its bottle and hop around. Swipe it with your sword to knock it over. Now pick it up and lob it against the wall.
Though it looks like you aren't damaging the boss, you actually are. Keep repeating this and, after enough wall lobs, the bottle will break.
The second phase starts after the bottle breaks, and sees the Genie split into two and circle around you. Then, one will materalise and throw a giant fireball at you.
When this happens, run away to avoid the splash damage, and then swipe your sword repeatedly in the Genie's direction as it lunges at you. Though it looks like you're about to be hit, your sword's length reaches further than the Genie's arms, so you'll hit it before it hits you.
Repeat this process - dodging the fireball when it appears, then waiting for the Genie to come to you to get an attack in - until the Genie is done for.
Our Zelda: Link's Awakening walkthrough and guide can help you with the critical path, including the Eagle's Tower and Turtle Rock dungeons. There's plenty to be done on the side, too - including Zelda Link's Awakening Heart Pieces, Zelda Secret Seashells and the Zelda Link's Awakening trading sequence. Finally, there's also the new Zelda Chamber Dungeons feature to unlock and complete.
When the Genie boss battle is over, grab the Heart Container and head next door to get the Conch Horn reward.
You'll then appear outside the dungeon. Before you head off, head back inside - you can now access the chest in the first room by moving all the pots, which contains a 50 Rupee piece.
When you are ready, it's time to head to Kanalet Castle.