The Legend of Zelda: Link's Awakening/Bottle Grotto

Boss: Genie
The trick to defeating this boss is to break the Genie's bottle, but you need to catch it first. To do so, either slash it or use your shield and let the bottle bounce off of you. When the bottle has stopped moving, pick it up using the Power Bracelet and throw it against a wall. Repeat this until the bottle breaks and releases the Genie. It will turn invisible, when it appears, be prepared to spin attack it before it can shoot fireballs at you. If you can interrupt its attacks, you should have no problem defeating it before it can kill you.