To defeat this Chu Chu Minish-sized, you’ll need the help of your Gust Jar. Use it at the boss’ feet to take away his support, and he’ll slowly sway, eventually dropping. When he’s on his side, run up to him and start swinging your sword.
He has no attacks, he just moves and jumps like a normal Chu Chu (which he is - you’re just really small). Stay out of his way and watch out when he falls on his side.
Gleerok is situated in the middle of a lava pit. His head follows you around the small arena, and he periodically spits fire at you. The idea is to roll around him until you have a clear shot on his body with the Cane of Pacci - shoot him, and his head will fall, creating a bridge to his back. Run up it and start slashing his back with your sword. When your hits stop registering, or he starts to sink back into the lava, quickly roll off him to avoid damage.
Gleerok’s real attacks come after you roll from his back. He’ll push lava to the sides of the arena while shaking rocks from the ceiling. Then, when he re-emerges, he’ll shoot fireballs at you which stay on the ground and can be removed with a sword slash or Gust Jar for a heart.
Mazaal, awfully similar to Ocarina of Time’s Bongo Bongo and The Wind Waker’s Gohdan, can be taken out in a similar way, with a Minish twist. While avoid his attacks, fire an arrow at his open hand to make its eye drop out.
Attack it with your sword to disable it, and do the same to the other hand. Then, shrink yourself and run into his head. Inside you’ll find a glowing pillar which you need to destroy with your sword. Repeat these steps, and the second time you enter his head, you’ll need to find the pillar with your Mole Mitts.
Until the third round, you just have to evade Mazaal’s hands, but then for your last run, you’ll need to avoid lasers from his head too.
For Octo, you need to repel the rocks he fires at you with your sword. After three successful returns, he’ll turn the arena into ice, and start spinning towards you. You’ll need to lead him one way and then roll around against his rotation to reach his green tail. Light your lantern and set him on fire to reset the arena. During the ice rounds, he’ll try and suck you in and freeze you, so your main objective is to stay out of the way of his mouth.
You need to go through this pattern three times, though the third time Octo will charge at you, and if he misses, he’ll hit the wall and knock rocks from the ceiling. He also spits black gas out, though you can use your lantern to see in the dark. During this third round, you simply need to return three rocks.
This battle is technically against two bosses. The idea is to use the panels on the red Gyorg’s back to line four Links up with his four open eyes, and to attack them. Then, the blue Gyorg will make a pass and you must jump on his back. One of his eyes will open at a time, and you should attack that eye while jumping over his rotating tail. Jump back on the red Gyorg when you have the chance, and repeat this pattern.
The blue Gyorg will begin to fire at you when you’re on the red Gyorg’s back, and small green Gyorg’s will try and knock you off when you’re on either Gyorg, but these can be dispatched with a couple of swipes.
This first form of Vaati is easy as long as you remember to stay near the top of the screen. The idea is to attack his eye pendant, but he’s surrounded by orbs that spin around him. They’re dispatched in a few hits of a sword, at which point you can go in and attack his eye. These orbs gain a barrier of protection, but you can suck these off with your Gust Jar.
After you’ve inflicted some damage, the orbs begin to fire lasers downwards and move to the side. The lasers are deadly, but if you’re to the top of the arena the orbs are extremely vulnerable to both your sword and Gust Jar.
The 8 orbs surrounding Vaati are small eyes that you need to open with your bow. You need to clone yourself using the four panels at the bottom of the arena in the pattern of his four open red eyes (the other four will turn light blue and stay closed when hit). Run up to the eyes and slash them until they disappear and Vaati falls to the ground. It doesn’t matter if you lose your clones, but you’ll inflict more damage if all four of you are attacking Vaati at once.
Vaati will litter the arena with spikey objects that hurt when you walk into them, so try and clear these with your Great Spin Slash, or it’ll be hard to manoeuvre all four Links. He also knocks rocks down from the ceiling, and fires electricity at you, but these are easily avoided.
Vaati’s final form is this armed behemoth. If you’re low on health, you’ll be pleased to know this is perhaps Vaati’s easiest form. Vaati will plunge his arms into the ground, and you need to roll out of the way when they re-emerge, and strike them with the Cane of Pacci. Then, Minish-size yourself and run into the arm. Take out the little spidery eye thing with a redder pupil than the others to destroy the arm. For the second arm, you need to repeat this, but also equip your lantern so you can actually see.
When you leave the arm, you’ll see his four smaller arms are open. Clone yourself and repel all of the four electric balls he shoots at you to stun him. Run to him with all four Links and use this window of opportunity to deal some serious damage.