Arrghus is the guardian of the second Crystal in the Swamp Palace in both The Legend of Zelda: A Link to the Past and The Legend of Zelda: A Link Between Worlds and the Eastern Temple in The Legend of Zelda: Four Swords Adventures. Arrghus is a mini-boss as well, known by its japanese name Wart, in the Great Bay Temple and the Secret Shrine in The Legend of Zelda: Majora's Mask.
Arrghus is a large, one-eyed jellyfish which is surrounded by several miniature polyps called Arrgi. The Arrghi and the creature's ability to float make him invulnerable to most attacks. He attacks by sending his Arrghi at Link. Link can destroy the Arrghi by pulling them towards him with his hookshot and slashing at them with his Master sword. When Link has defeated all of the Arrgi, Arrghus launches into the air and attempts to crash down upon Link. It then speeds across the shallow water of the room, and in this state it is unprotected and can be attacked with the Master Sword or the Bow. If Link has dealt enough damage, Arrghus wil explode.
The orange Arrghus is the guardian of the Green Four Sword in the Palace of the Four Sword, an additional dungeon created for the Game Boy Advance version Past". Unlinke the original Arrghus, this version is surrounded by little jelyfish. He is more resiliant and able to deal more damage the his original form, and the little jellyfish will sometimes unleash their electricity when Link pulls them away from the monster. The rest of the fight is the same as its original counterpart.