A Link to the Past - Boss Guide
Armos Knights (Eastern Palace)
At the start of the fight, six knights will appear and circle around the room. Just avoid thier movement, and shoot them with arrows - three arrows will kill one of them. Occasionally the knights will group up and charge down the room, use this opportunity to easily shoot 3 arrows into one and kill it. When there is only one knight left it will turn red, and it will move around the room trying to jump onto you. Avoid this, and then just shoot it down with arrows, or use your sword if you have no arrows left.
Lamolas (Desert Palace)
When one of the giant worms is about to jump out the sand, be careful since four rocks will fly accross the room once it does appear. Swipe each one in the head with your sword to kill them. When there is just one giant worm left, it will shoot out a whole load more rocks then normal when jumping out the sand, so keep your distance before it jumps to prevent getting hit.
Moldorm (Tower of Hera)
To defeat Moldorm, you have to hit the end of it's tail while avoiding the rest of it's body. Make sure he isn't near you when you have to run past a ledge, since you will get knocked down and the fight will be reset. Also, after you have hit Moldorm a few times, it's movement speed will increase rapidly, so hit the tail quickly once more to kill it.
Agahnim (Hyrule Caslte)
Agahnim has three attacks. When Agahnim appears, after his shadow has been moving accross the room, position yourself facing him, but at a distance. His first attack will send an orb of magic flying towards you - hit it with your sword to reflect it back at him, and damage him. His second attack will send a group of smaller orbs towards you, which you must dodge. His third attack will send a bolt of lightning towards you, it is unavoidable, but predictable - Agahnim will only cast it if he is at the top of the room, facing south, so move out of his line of sight when that happens.
Helmassaur King (Dark Palace)
Perhaps the most annoying boss in the game, your first job is to smash Helmassaur's mask off with your magic hammer, or by using bombs. Once the mask is broken off, you need to hit the green jewel on his forehead until you kill him. When it's tails starts to waggle quickly, run to a corner in the room to avoid getting hit by it. He also has a fireball attack, in which he sends one fireball, which splits into four, and then all those balls split into another four. These can be tricky to dodge, and you may die a few times before you finally take this boss down.
Arrghus (Swamp palace)
At first, you will see Arrghus covered by a bunch of cloudy spawns. Avoid Arrghus and use your hookshot to draw the cloud things away from it, promptly using your sword to destroy each one. After they're all dead, Arrghus will start running about. Use your sword/arrows to dispatch him from there. When Arrghus takes a big leap, you will notice where he is going to land (indicated by his shadow that appears on the ground). The best way to avoid his jump attack is to dash away from him with the Pegasus boots.
Mothula (Skull Palace)
There isn't much to say about this boss, since the obstacles of this boss are physical challenges rather then built-in weaknesses. You have two choices here; either kill Mothula with your sword, or use the Rod of Fire. The sword method requires fewer hits to kill Mothula, but the Rod of Fire method also has it's advantages - since you attack from a distance, it's easier to position yourself in avoiding the moving spikes that go around the room.
Blind the Theif (Theif's Lair)
To get Blind out in it's true form, take the maiden into the room in which there is light coming from the roof at the center. Have her walk into this patch of light, then she will transform into Blind the Theif. Hit Blind's head until it comes off, at which point another head will grow shortly after. After he has lost his third head, he will die. Each head Blind loses will fly around the room and shoot fireballs at you, so be careful.
Kholdstare (Ice Palace)
Use the Fire Rod (or Bombos Medallion) to melt the ice block down. From there, three floating eyeball monsters will emerge. There are two things to avoid: firstly the eye monsters, and secondly there will also be ice periodically falling from the cieling. Avoid these things whilst striking the eyes with your sword or shooting them with the fire rod. A good general tactic is to try and 'kite' the monsters around the room by running into uninhabited spaces.
Viterous (Misery Mire)
This boss isn't too hard. As you run into the room you will notice one big eyeball surrounded by many smaller eyeballs. The smaller eyeballs will come towards you, you can shoot them from a distance with your arrows or hit them with your sword. Whilst you are killing the little eyes pay attention to the big eye, as it will periodically emerge from the goo and shoot a powerful bolt of lightning. Before the attack takes place the eye will aim itself, so if it aims to the right it's attack will strike to the right of the room, and so on. After enough little eyes are defeated, the big eye will pop out, from there just use your sword/arrows to kill him.
Trinexx (Turtle Rock)
You will need the Fire and Ice rods in this fight, and it is reccomended that you stock up on magic potions. The creature has three heads: notice the red and blue heads. You should kill the blue head with your Fire Rod, then the red head with your Ice Rod. It is also possible to hit the heads with your sword, but using the rods allows for a ranged kill. After both the heads are gone, a snake-like creature will emerge from the big rock, hit it's head with your sword until it dies. One tip here is to stand next to the big rock as it is being depleted and use your sword spin attack the moment the snake emerges.
Agahnim (Ganon's Tower)
This fight is similar to your first encounter with Agahnim, except now there are three Agahnims! However, two of them are fake illusions and only one is the real Agahnim. It's easy to see who the real Agahnim is since the fake counterparts are faded. Each Agahnim will attack you with flying orbs of magic, and the goal is to use your sword on any of them to redirect the attack back to the real Agahnim.
Ganon (Ganon's Tower)
There are a number of distinct stages to this battle. During each stage the aim is to hit Ganon with your sword as much as possible. The battle progresses through each stage after you inflict a certain amount of damage.
Stage 1: Ganon will throw his weapon accross the room, and will teleport accross the room to reclaim it. The attack is very easy to avoid, you can tell if he's about to throw his weapon when he starts to spin it.
Stage 2: When Ganon starts spinning his weapon he will not throw it, but instead he will summon a circle of fire which will then be shot accross the room in all directions. Moving far away from Ganon makes this attack easier to avoid.
Stage 3: Ganon will teleport accross the room and when he appears, he will summon a ring of fire around him. You will need to take note of where Ganon appears to be teleporting to, so that he will appear right next to you, where you will slash him before he can create his ring of fire. Each time you strike Ganon during this phase, he will stomp on the ground causing a row of floor tiles around the edge of the room to collapse.
Stage 4: Stage four begins after four rows of tiles have been depleted by Ganon. He will put out the lights, making him invisible. He will continue teleporting around the room, but now he will shoot fire at you. Use your fire rod to re-light the torches at the edges of the room and once Ganon re-appears, strike him with your sword. Striking Ganon will cause him to become temporarily stunned, at which point you must damage him by shooting him with a Silver Arrow. You will need to shoot Ganon a total of four times, and then he will finally be defeated.
Note: To see the battle in action check out this youtube video.