Bilocyte

The Ocular Parasite Bilocyte is a large parasite that appears in SS undefined. It enters into and possesses the Great Sky Spirit Levias, who lives in Thunderhead.

Properties
Bilocyte is a large red parasite that possesses Levias, controlling his body and mind and making the Sky Spirit much more aggresive than usual. It has a single large head that contains a vulnerable eyeball and two frills, its two main weaknesses. It also has many tentacles, each holding an eye at the end, extended from holes along Levias's 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 Levias's body. Alternatively, using the Bow and a well-aimed arrow, Link can shoot down the tentacles from atop Levias. Once all the tentacles are destroyed, a single eyeball will attack Link from its position rooted inside Levias's blowhole.

This larger eyeball is not another tentacle, but the head of the parasite known as Bilocyte. Link must land atop Levias's head to do battle. Bilocyte attacks Link by spitting out green projectiles from its mouth, which Link must repel in such a way that they impact Bilocyte's frills, closing them. After impacting both frills, Link can either reflect more projectiles into Bilocyte's eye or use a Skyward Strike on it to bring Bilocyte down, allowing Link to release a barrage of sword strikes upon it. After repeating this process a few more times Bilocyte is destroyed and Levias is restored.

Trivia

 * Levias and Bilocyte are the only bosses that cannot be challenged in the Thunder Dragon Lanayru's Lightning Round.
 * Bilocyte seems to bear slight resemblance to Eye plants in Phantom Hourglass.