Go South then right to the next screen and talk to the man. Collect the wood he asks for and give it to him. It's easy to do even though it doesn't show on the map. Go back to the screen you came from and walk around its edge counter-clockwise until you see the sled. Save your game, then hop on the sled.
Dodge trees until you come to a stop. When you do, save again. Kill the mice with your slingshot and find Merlin. He'll ask you five (easy) questions. Get three or four right and you may continue on. Try for five. If you don't get them all right, reset and try again until you do. If you succeed Merlin will give you a heart.
A cave will open up when you are done talking to Merlin. Go inside it. Go into the bottom right cave, talk to Merlin again, then get all the tablets. once you have done so talk to Merlin again. Go to the cross of stones. They will be laid out as follows.
Walk over them in the following order: 1 → 3 → 5 → 2 → 3 → 4 → 5 → 3 → 1 → 4 → 3 → 2. Enter the door that opens up and kill the magician. He's one of the annoying bosses, but you can sometimes knock his shots back with your sword.