you find all the monkeys
when you get all 4 monkeys, go back to where the baboon cut the bridge, then the monkeys will let you swing on them, the mini-boss is here, which is the baboon. I hope this helped you! Note: the baboon is only evil because a bug is on his head and is controlling him, when you defeat him the bug will die and he will run away, he helps you in the boss fight.
If its the Baboon Ook, then he is the Mini-Boss in Forest Temple.
Where is the mini boss in the Forest Temple? once you have 4 of the monkeys, go back to the room where the baboon cut the bridge and the monkeys will swing you across. to defeat the baboon keep rolling into the totem poles when the baboon stops to throw the boomerang at you until he falls of then keep hitting its butt. repeat until defeated. you will get the gale boomerang.
You get it in the sky temple when you beat the mini boss.
Kill the mini boss on the Sandship
You need to be more specific about what mini-boss and what Zelda game. However, there is a mini-boss within each dungeon, providing a useful item after defeat. I would recommend using walkthroughs for more details.
You find it after defeating the mini-boss in the Goron Mines (2nd dungeon)
a fourth monkey, and the mini boss. then more monkeys and the boss.
8 in all, including the four you have to find before the mini-boss
deffet the monkey mini boss
You have to find it in the temple of time, which is hidden in the sacred forest. if memory serves, you will find it after you defeat the mini boss.
You have to defeat the baboon mini boss, he'll drop his boomerang and you'll get it.