Bilocyte

Ocular Parasite Bilocyte is the large parasite that appears in Skyward Sword and has entered into and possessed the Great Sky Spirit Levias, and is also the boss of Thunderhead.

Appearance and Features
Bilocyte is a large red parasite that has recently possessed Levias making the Sky Spirit much more aggresive then normal. Sporting a single large head holding a large eyeball and two leopard printed frills its two main weaknesses. It also holds many tentacles holding an eye at the end of each, going through many of Levia's holes on his body.

To defeat Bilocyte, Link first has to use his Crimson Loftwing to Spiral Charge into the eyeball at the end of each tentacle hanging out of Levia's body, once all of the tentacles are destroyed. Additionionally, using the Bow and a well-aimed arrow, you can shoot down the tentacles from a top Levias. A single eyeball will be seen hiding in Levia's blowhole.

Upon landing Link will find out that its not another tentacle but the head of the parasite know as Bilocyte. Bilocyte attacks Link by spitting out large green balls of gunk out of its mouth, which Link has to position his sword and knock them back at one of Bilocyte's frills closing it. After shutting both seals, Link can either hit more green gunk at Bilocyte's eye or instead use a Skyward Strike on the creature's eye to bring Bilocyte down instantly. Allowing Link to release a barrage of sword strikes at its eye. After repeating this process a few more times Bilocyte is destroyed and Levias is unpossessed.

Trivia

 * Strangely, Bilocyte is the only boss that's not fought again in Thunder Dragon Lanayru's Lightning Round.