Zaganaga is the boss of the Desert Palace, a dungeon in Hyrule in The Legend of Zelda: A Link Between Worlds. Although the Desert Palace is in Hyrule, the battle takes place in Misery Mire, in Lorule.
Zaganaga is arguably one of the most difficult bosses in the game due to its tricky battle pattern and high resilience, so preparation such as Fairies or Red Potions is advised. At first, Zaganaga does nothing except teleport itself from one platform to another, so Link must use the Sand Rod to create a pathway between the platforms to get close and inflict damage. Once enough damage is inflicted, Zaganaga will spit Peahats that fly and ricochet across the entire battlefield, serving as a major nuisance given Link's limited movement without the Sand Rod, and prompting Link to face the miniatures while being mindful of the surroundings and attempting to inflict damage on the monster.
Once more damage is inflicted, Zaganaga reveals its true self with several eyes. During this form he becomes much more frustrating as he now will aim at Link and spit a torrent of sand at him causing him large damage if he does not escape, while also being capable of pushing him into the sand to further increase damage. This phase can be difficult given Zaganaga's large amount of health, and the threat of the Peahats is ever present. Two tips are best used to inflict the most damage to Zaganaga: The first is that if he is too far away yet on a direct trajectory from Link, to use projectile weapons like the Bow or, if upgraded, the Hookshot. The second is for when Zaganaga is in the platforms closest to either edge of the battlefield, due to its proximity to safe land, Link can create a path with the Sand Rod, and hack away at the monster, then turn back. At this point Zaganaga will spit sand but it will be where Link is no longer present; then create another path to get close to Zaganaga and slash as the monster made a blind spot easily exploited.