Arrghus

Arrghus is the guardian of the Second Crystal in the second dungeon in the Dark World of The Legend of Zelda: A Link to the Past.

Arrghus is a large, one-eyed jellyfish which is surrounded by several miniature polyps named Arrgi. He will often flare them out in an attack. To defeat him, these must first be destroyed. They can be pulled away with the Hookshot, and then slashed with the Master Sword. When all of the Arrgi are gone, Arrghus starts crawling over the ground very fast, and also jumps up high in the air in an attempt to squash Link. In this state, he is unprotected and can be easily destroyed using Link's sword. After his destruction, Link receives a Heart Container and the Second Crystal in which one of the seven maidens is imprisoned. In the Gameboy advance version Arrgus reappears. This time instead of using Arrgi he uses electric Bari. When you snag them with your hookshot you have to check to see if they are electric before attacking or risk getting a powerful shock.

Stone Arrghus
The Stone Arrghus appears as the boss of Eastern Temple in Four Swords Adventures. To defeat the stone version of this Boss, Link must use his Boomerang to pull the rocks to him then hack them with the sword once all the small rocks have been destroyed, the large eye attacks Link. Once it has been hacked at enough, it will disintegrate and leave Link with the Yellow Maiden.

Wart
Wart is a very similar miniboss that makes an appearance in Majora's Mask. He is the mini boss in the Great Bay Temple. Interestingly enough, he is defeated in the same exact manner, with the exception that arrows must be used on it's single eye.