Arrghus

Arrghus (ワート, Wart) is the guardian of the second crystal in the second dungeon in the Dark World of A Link to the Past.

Arrghus is a large, one-eyed jellyfish which is surrounded by several miniature polyps called 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 speeding across the floor, and occasionally jumps 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 Game Boy Advance version Arrghus reappears, this time using electric Bari in the place of Arrgi. Before you snag them with your hookshot, you must 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 and 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 as the mini-boss of Great Bay Temple. Interestingly enough, he is defeated in the same exact manner as Arrghus in A Link to the Past. Also worthy of mentioning, is that in the Japanese version of A Link to the Past, Arrghus's name is "Wart"; the reason behind the switch and whether they might be the same enemy is unknown.