The Legend of Zelda: Link's Awakening/Color Dungeon

The Color Dungeon contains a small yet intricate set of puzzles that you could spend hours working out if you don't pay close attention to the patterns.

First of all go to the Mabe Village library. You'll notice a book on the top of the centre shelf. Equip the Pegasus Boots and ram into the shelves, knocking the book down in the process.

Miniboss #1: Giant Buzz Blob
And now, you'll fight... the uber-sized Giant Buzz Blob! He says the sword can't harm him. Remember how the blue Stalfos told you to have Magic Powder with you? Use it. It will damage Giant Buzz Blob when you sprinkle it on him. After about five doses, he falls. Head left, and you'll get the Nightmare Key.

Miniboss #2: Stone Hinox
And now it's miniboss number two: Stone Hinox! He is quite tough, and drops boulder after boulder at you, and toss you if you get too close. He is basically a Hinox, but with a stone-armored body. It will take many hits to defeat him, but if you have the Fire Rod, he'll go down in two hits.

Boss: Giant Hardhat Beetle
The boss is Giant Hardhat Beetle. "Blue is safe. Yellow is caution. Red is danger." This line he says refers to his own health. Simply keep him from turning back to blue. The darker he gets, the closer to victory. When he's red, hit him one final time to kill him. The Fire Rod should make quick work of him, if you have it.