Giant Green ChuChu
A simple boss. Just use the Gust Jar on his tentacle leg-supports (they turn red when you use the gust jar upon them) until he makes a sound and starts teetering. Stand to his side, then when he falls get out of the way and then slash him like mad. The Giant ChuChu will jump and teeter this way and that, and this jumping increases as it loses more and more health - peaking just before you've killed him.
Gleerok
Get to his side and use the Cane of Pacci on his shell. Then climb his neck and slash his body till he starts going into the lava. If you get low on health, use your sword on the flames he spits out for hearts. After slashing its back, hide near the closest corner because the lava will rise and rocks will fall. You have to do this 3 times. After you do it once, Gleerok will start shooting a lot more fireballs, covering a whole quarter of the arena in fire.
Giant Blue ChuChu
Weak: Gust Jar
Mazaal
Weak: Arrows in Hands/Pillars inside
Giant Octorok
Weak: Lantern
Gyorg
Weak: Roc's Cape + Duplication
Vaati 1
Vaati 1's weak point is his eye. During the battle, he will send out eyes covered in black balls that shoot lasers. Use the gust jar to suck the balls and they will become vulnerable for an attack.
Vaati 2
Weak: Duplication + Sword + Arrows
Vaati 3
The Cane of Pacci and the Sword are the weapons that will be needed. The arms will attack you. Use the Cane of Pacci to uncover the hole, shrink yourself in order to get in. Once in, destroy a monster in and his arm will be destroyed. Do this to both arms and he will start using his four eyes. They will shoot at you. Duplicate yourself into four and wait for an attack. When he attacks you, swing your sword and reflect it back to his eyes. He will now be vulnerable for an attack at his big eye.