The following A Link to the Past Bosses guide covers every boss in A Link to the Past and provides an image of each in order to help with visually finding which boss you need help beating.
Ball and Chain Trooper
The Ball and Chain Trooper is a knight with a chain and spiked ball. He will constantly swing the ball and chain at you so watch out. There are a few ways in which you can kill it. You could use your boomerang to stun him and then use your sword to strike him. Another more simple way would be to go into the cell and pick up a jar. Then you wait until he swings the ball and chain at you but misses. You then have to run up and throw the jar at him. Repeat either process a few times and he will be defeated. After you defeat him you will get the big key which unlocks the cell that Zelda and a treasure chest are in.
Armos Knights
The Armos Knights are six blue knights. They will take two stages to defeat. Use your arrows to shoot each of the first five three times. Once the five are gone the sixth one will turn red and then start jumping around trying to land on you. You can use your arrows to kill him or you can also use your sword.
Lanmolas
The Lanmolas are three giant worms. They take a couple stages to defeat. They will start out be jumping in and out of the ground every few seconds while shooting out four rocks each time. There are a few ways you could use to defeat them. You can use bombs, arrows, or your sword. I find it the easiest to hit them with your sword but it is the riskiest but best method. You will see the ground shaking around where each one will come up. All you got to do is go around it and hit him when he comes out. After the first two are down, the third one will shoot out eight rocks. You will just use the method here but it is more tricky with the higher amount of rocks. If you can not seem to beat them then bring a bottle with a fairy in it.
Moldorm
Moldorm is a worm like boss that can be a little frustrating at times. The only way to damage him is by hitting his tail. You also have to fight him on a ledge where you can fall off, and if you fall off, he gains back all his power. The way I find best is to keep your distance from him. Stay on the right side of the small gap. Go after him when he is going away from you. You need to go in and hit him, then run. As you damage him he will speed up, which makes it more difficult.
Agahnim
To defeat Agahnim, you will have to use his own magic against him. He will go around the room and shoot different things out at you. He will shoot one of three things: a blue circle, lightening, or a small glowing ball. What you must do is dodge the blue circles and the lightening. When he shoots the glowing ball at you deflect it it back at him with either your sword or the bug-catching net. After a few hits he will be defeated.
Helmasaur
Helmasaur is a two stage boss. The first stage you must break off his mask with either three bombs or the hammer. Once the mask breaks off it will reveal a weak point, which is a glowing green circle that was covered earlier. You can use either your sword to hit it or your arrows. Other then its tail you should have no problems defeating it.
Arrghus
Arrghus is a two stage boss. At the beginning he will be surrounded by a bunch of Arrgi. You have to use your hookshot to pull one off and kill it. You have to defeat all the Arrgi one by one. You should also try to stay as far away as you can. Once all the Arrgi are gone, he will try and jump and land on top of you. You just need to move to the side and hit him with your sword when he lands. The hammer works also but it is harder to hit him with. After a few hits he should be defeated.
Mothula
Mothula is damaged most by the fire rod. So keep your distance from it and shoot it with the fire rod. If you run out of magic you can use your sword, but it is much harder. It will shoot some sort of a ray at you, just try to dodge it. There are also spikes moving across the floor you need to try to dodge as well. I would suggest having some red and green potions just in case.
Blind
Blind will move around one side of the room. You will need to hit his head three times. Once you hit it three times it will start flying around the room and another head will grow on him. The flying head will shoot lasers at you while you have to defeat the other head. Once you defeat the other head it will start flying around the room like the other one and another head will grow on him. You just need to defeat this head to defeat the boss. I would suggest bringing a fairy or two if at all possible.
Kholdstare
This fight starts out with Kholdstare inside of an ice block and ice will fall from the ceiling. You just need to use your fire rod eight times until the ice cracks and Kholdstare splits into three. Now you can use your sword to hit it or the fire rod. Just hit each eye six times untill all of them are gone to defeat this boss. I would suggests bringing a green potion in case you run out of magic.
Vitreous
This is another two stage boss. The first stage will have Vitreous's eyes coming out about four at a time to try an attack. Every once in awhile Vitreous will shoot lightening out at you. Just take out the small eyes with your sword. Once all the eyes are gone, Vitreous will come out and start moving around the room. You just need to use your sword against him. After a few hits he will be defeated.
Trinexx
Trinexx a three headed rock creature. The start of the fight you will be fighting the two top heads. The red head is for fire and the blue head is for ice. So you have to use the ice rod on the red head and the fire rod on the blue head. Start off by taking out the blue head first, because it will use ice that goes on the floor and makes it slippery. Once the blue head is gone, use your ice rod to defeat the red head. I would suggest bring at least one bottle of green potion in case you run out of magic. Well once the two heads are gone, the rock will break and the third head will come alive. It will then get up and start flying around the room. One of the boulders on its body will also start to glow. Strike it with your sword, while trying to dodge its attack. Hit it three times with your sword to defeat it.
Agahnim
The second fight against Agahnim is very similar to the first one. This time though, there are three Agahnims. You can tell which is the real one because the other two are much lighter. The method to killing Agahnim is the same as before. You just have to use your sword to reflect the circle, glowing ball back at him. You can also use the other two Agahnims magic against the real one as well. This battle is a lot harder then the first one because the fake Agahnims can hurt you as well. After you defeat him, he will transform into a bat and fly to the Pyramid located at the center of the Dark World.
Ganon
There are several stages to Ganon. The first few will occur when the lights are still on. He will wave his pitchfork and firebats will form and chase after you. Just try dodging them and hitting Ganon with your sword. The Golden Sword will make this battle a lot easier, so I suggest you have it. Just keep striking him. He will all try throwing his pitchfork at you and then transporting to the other side to catch it. You just got to keep going at him with your sword. He will eventually start to jump and pound the ground. The outer row of tiles will then start falling one side at a time as he continues to jump and pound the ground.
After the outer row of tiles fall he will put out the torches so it will be dark and he will be invisible. You will need to use your fire rod and light the torches. After that quickly hit Ganon with your sword. He will turn blue. You need to then use your silver arrows and hit him with them. The torches will go out after a certain amount of time. Just relight them and hit him with the sword and then the silver arrow. You have hit him with about four silver arrows to beat him. After defeating him a platform will appear at the top of the screen. Just go in there and claim the triforce.
