If you use the Ice Rod to freeze any monster, and then hit it with the Hammer, you will most likely gain magic.
If you sprinkle the Magic Powder on the Red Anti-Fairies, they will turn into a fairy.
Early Golden Sword
There is a way to get the Golden Sword before even defeating the Helmasaur King. First off, get the Hammer from the Dark Palace, then the Hookshot from the Swamp Palace. Get the Fire Rod from the Skull Woods and the Titan's Mitt from Gargoyle's Domain. Get the Flute from the Flute Boy and make sure that you have access to the bird. Defeat the bosses in the Ice Palace and Misery Mire and the Super Bomb will be for sale at the Bomb Shop. Blow up the wall in the pyramid and get both the Golden Sword and Silver Arrows.
Unlimited Magic Potion
If you go to one of the Great Fairy Fountains and throw in an empty bottle, the Fairy will give in return a bottle filled with Green Potion.
The Magic Cape is a good item to use when faced with danger. You can walk over spikes without getting hurt and walk through the blue bumpers.
Double Magic Points
Fall into the hole in the same area as the Smithery (you need the Hammer). Use the Magic Powder on the Alter to awaken a demon who will cut MP usage by 1/2 (or double the magic points).