The Frog Toad is the miniboss of the Lakebed Temple. After defeating it, you get the Clawshot, which is the dungeon item.
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.
The Deku Toad Mini-Boss is located within the Lakebed Temple, and for defeating him you get a Clawshot. Use a walkthrough for better details.
a fourth monkey, and the mini boss. then more monkeys and the boss.
deffet the monkey mini boss
you find all the monkeys
a white monkey with a golden mask
Yes. He is the mini boss in the water temple.
You finish off the forest temple mini boss
battle the mini boss at city in the skys
You get it in the sky temple when you beat the mini boss.
Kill the mini boss on the Sandship
The boss key can be acquired in several different ways but usually you will acquire it in a chest. If not this method then you usually must defeat a mini boss.