Well, this is my first fight in a while, and my fights were generally bad either way, so here goes nothing! Both are found after a fight with Phantom Ganon, the Megaton Hammer found in the Fire Temple, the dungeon after the Forest Temple where you fight Phantom Ganon. The Skull Hammer found in the Forsaken Fortress after fighting Phantom Ganon. Both are required to progress in the Dungeon you find them in, the Megaton Hammer to depress the rusted switches, and the Skull Hammer to smash the wooden peg looking things. Both are used to fight the dungeon boss in a similar manner. The Megaton Hammer is used to smash Volvagia's skull/mask thing. Skull Hammer to smash Helmaroc King's mask. And both have minimal usage outside of said dungeons (correct me if I'm wrong on that case, haven't played W