Horsehead: His weak spot is, obviously, his head. Use the shield spell bofore you fight him. You have to jump, then go for his head, but get out of the way fast. He attacks with a club.
Helmethead: He's probably the easiest boss to beat. Again, you have to go for his head, but they will come off, then shoot fireballs at you. Take out three heads and you've got him!
Ironknuckle: This iron soldier rides a ghost horse. Use the downward thrust a few times, and the horse will run away. Now you can defeat the soldier normally, but watch out because the blue ones throw swords!
Carock: A very powerful magician who has mastered the dissappearing act. Make sure you use the Reflect spell, then when he uses his magic, sit down & reflect it back to him.
Gooma: I have NO idea what this thing is, but you have to hit him bolow the belt. Watch out for his mace.
Barba: Make sure you use the shield and jump spells before you begin. This dragon will come up out of the lava and shoot fireballs at you. Go for his head, then jump out of the way when he shoots fireballs at you.
Thunderbird: Make sure you have LOTS OF MAGIC!!!!! When he come on the screen, use the Thunder spell. (You can't hurt him when he's red) Then, use jump so you can hit him in the face. Each time you hit him, he will shoot more fireballs. It's not as easy as it looks.
Link's Shadow: He's the hardest boss in the game. The best thing to do is sit in a corner and start swinging your sword. Make sure you have magic to refill your life. If you die while battling Link's Shadow, you will not have to defeat Thunderbird again.