Bilocyte

is a SS: in SS undefined. It is a large parasite that infiltrates and possesses Levias, who lives inside the giant Thunderhead near Skyloft.

Characteristics
Bilocyte is a large, red parasite that possesses Levias, controlling his body and mind and making the Sky Spirit much more aggressive 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 must first use his 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 of the tentacles have been 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. When it appears, Link must land atop Levias's head to lure it out to battle. Bilocyte attacks Link by spitting green projectiles at him from its mouth, which Link must deflect with his Sword towards Bilocyte's frills, closing them. After hitting both frills with the parasite's own projectiles, Link can either reflect more projectiles into Bilocyte's eye, use a Skyward Strike, or fire an arrow at it to bring it down, allowing Link to release a barrage of Sword strikes on the creature. After repeating this process a few more times, Bilocyte is destroyed and Levias is restored to his senses.

Trivia

 * Levias and Bilocyte are the only bosses that cannot be challenged in the Thunder Dragon's Lightning Round.