The Guard in the Hyrule Castle with the mace can be defeated using your boomerang and sword or using the pots from inside one of the cells.
The Armos Knights guarding the Pendant of Courage look like six bouncing statues. The Armos Knights can be defeated with three Arrows each. If you run out of Arrows, switch to the Sword and swing for all you're worth. One Armos Knight takes 12 strikes from the Sword to be defeated.
The Lanmolas that guard the Pendant of Power are three large green worms that shoot out of the sand floor and dive back down again. To defeat them, power up your Sword by holding the B Button and use the Whirling Blade technique on the worms' heads. Each of the Lanmolas will require eight hits from the sword before they subside into the dust forever.
Moldorm guards the Pendant of Wisdom and is a large yellow worm with five round sections, whose only vulnerable point is at the tip of its tail. Stand at a safe distance from the edges of the platform and hold the B Button to charge up your Sword. Once your Sword is fully charged, release the B Button to perform the Whirling Blade technique. Six hits to Moldorm's tail will put him away for good! Be careful -- if you fall off the platform, Moldorm will regain all his energy. If this happens, you will have to climb back up and start again. All the hits you scored against him will have been healed, and you will have to hit him another six times without falling off the edge.
The only way to defeat Agahnim is to use his own magic against him. To do this, swing your Master Sword at the fireballs Agahnim throws to deflect them back to him. Occasionally, Agahnim will stand at the top of the room and unleash a tremendous lightning attack. To avoid being hit, stand against one of the side walls in the room. Good luck!
Helmasaur is a red four legged monster with a spiked tail that he lashes at you. He has a weak point in the middle of his forehead that he carefully protects with a strong purple mask. Use three Bombs or your Hammer to break through the mask. Finish him off by attacking the gem in the center of his head with your Sword or Arrows.
Arrghus is a large, one-eyed jellyfish with a a thick coating of pink puff balls. To defeat him, you must destroy the pink balls one at a time. Do this by using your Hookshot to pull a pink ball near you and hit it with your sword until it disappears. Repeat this process until you have destroyed all the pink puff balls. Once this is done, you must hit Arrghus eight times with your Sword or four times with the Hammer to defeat him.
Mothula is a giant moth that shoots rings of fire at you. Before you go into battle with Mothula, you should have one Magic Medicine bottle (the blue one) and the 1/2 symbol above your Magic Meter. Shoot Mothula repeatedly with the Fire Rod as you try to avoid the spike traps in his room. If you are having trouble doing avoiding the traps, use the Cane of Byrna for protection. Mothula will take 15 shots from the Fire Rod or eight hits from your Sword to be defeated.
Blind the Thief is a demon that moves around the room shooting red lasers at Link. To defeat him, stand behind the square patch of sunlight and swing your Sword at him whenever he is nearby. While he's circling inside the room, move left and right to dodge his laser attacks. Keep hitting his head until a total of three heads have fallen off. Each head takes three hits from the Sword or Hammer.
Kholdstare looks like an eye frozen inside a huge chunk of ice. To defeat him, thaw him with eight shots of your Fire Rod while avoiding his icy attacks. After the eighth shot, he will break into three eyeballs that bounce around the room. Hit each eyeball six times with the Sword to defeat it.
Vitreous is a large eyeball surrounded by a bunch of smaller eyes that fly at you. To defeat him, stand in the bottom-left or bottom-right corner of the room to avoid his lightning attacks. Destroy the small eyes that fly at you. The Whirling Blade Technique works the best. After defeating all the small eyes, the big eye will start to bounce around. Use the Whirling Blade Technique again to finish him off.
To defeat Trinexx, you must combine the powers of the Fire Rod, the Ice Rod and your Sword. Use the Fire Rod on Trinexx's blue head to stun it, then hit it with your Sword. Repeat this until the blue head is defeated. Then, use the Ice Rod on Trinexx's red head to stun it, then hit it with your Sword until it also disappears. Trinexx will then change into a worm-like creature with a flashing circle near the center of its body. Hit this flashing area three times with the Sword to defeat Trinexx once and for all.
When you fight Agahnim in the Dark World, he brings along two friends. You can tell who the real Agahnim is because the other two are slightly hazy. Attack the real Agahnim by using his own magic against him. Swing your Master Sword at the fireballs he throws to reflect their evil power back at his image. Caution: Agahnim will occasionally stand at the top of the room and unleash a ferocious lightning attack. Stand to one side of the wizard to safely avoid it. Once he's gone, you're off to Gannon!
To defeat Gannon, you must use the Silver Arrows when he is weak. Unfortunately, he isn't a push-over. The battle will be a long and difficult one. Avoid Gannon's attacks while hitting him with your Sword as often as you can. After a while, Gannon will attempt to put out the lights in the room. When this happens, light BOTH pots with your Fire Rod (this is very important!), then hit Gannon with the Sword to turn him blue. Hit him with the Silver Arrows when he's blue, then wait for him to recover. Repeat the process of lighting the braziers and shooting Gannon with the Silver Arrows three more times. Once you've defeated him, you have completed your quest. Congratulations!