Wonder Boy: The Dragon's Trap

Story-related; cannot be missed. 

This is the final boss. To make this even easier, than he already is, farm lightning magic before the fight. Once he flies in a place where you can't hit him, use lightning and he'll move out and back in from another angle. If you really want, you could just spam lightning until he is dead, however farming that much probably takes more time and effort than just beating the boss normally.

Also, if you have the Tasmanian sword, switch to Lion form before the fight. Remember to switch back to Legendary or Gallic sword, because the Tasmanian sword does very little damage to the boss.