Killer B's Jinchūriki Forms

Killer Bee is the jinchūriki of the Eight-Tailed Giant Ox, and is therefore capable of transforming into various forms that resembles his tailed beast, until he finally takes on the complete form of the Eight-Tails. So far, he has displayed a greater variety of forms than any other jinchūriki. Unlike Naruto and Gaara, he has full control of the Eight-Tails and his transformations. According to some Kumogakure shinobi who passed by and saw his full transformation, the Raikage had forbidden him to transform.

Version 1
Using his own chakra, Killer Bee can freely and quickly form a demon cloak that surrounds his body. Once activated, his incisors and nails grow long and sharp. The cloak itself gives Killer Bee paws of chakra around his hands and horns on his head. He can also create an additional set of horns on his arms to use for his Lariat attack. Unlike Naruto's tailed transformations, the chakra cloak does not attack on its own.

Killer Bee can produce up to eight tails in his version 1 transformation. He enters a three-tailed form during his fight with Taka, and a four and seven-tailed transformation at different points during his battle with Kisame. Kisame's Samehada is able to absorb up to six of these tails at a time. Like Naruto's first three transformations, these tails are transparent. Other than an incremental increase to Killer Bee's strength and speed, however, there are no obvious differences between the number of tails.

Version 2
By tapping into the Eight-Tails' chakra reserves, Killer Bee can enter "version 2" transformations. As stated by Sabu this is done by turning the chakra into a human shape. These are meant to give him an edge in battle without completely unleashing the Eight Tails, as that would endanger anyone around him. A version 2 chakra cloak is much darker than version 1 (similar to Naruto's four-tailed form and upwards), turns his feet into hooves, and elongates the horns on his head. While in this form Bee looks much more muscular than he did before and if necessary he can create bones out of chakra, such as a bull's skull, to increase the strength of his attacks.

Killer Bee has been seen in a seven-tailed and eight-tailed version 2 transformation thus far. When struck by Samehada, only the Eight-Tails' chakra is absorbed, so Killer Bee reverts to a version 1 form with the same number of tails.

Full Eight-Tailed Transformation
While fighting Sasuke and his team, Killer Bee managed to wound Sasuke long enough to transform into the Eight-Tails' full form, in which his skin is destroyed in a similar fashion of Naruto when he reaches the fourth tail and above. In this form, he takes on the appearance of the Eight-Tails itself, rather than just a cloak, appearing like a huge ox-like creature with eight octopus tentacles as its tails and four horns on his head, one of which is broken. Like with his previous transformations, he seems to be in full control of this form, though to what extent is still unknown.

In this form, he is able to create a huge sphere of chakra in front of his mouth similar to Naruto's Four-Tailed Fox Menacing Ball, but he releases it as a widespread blast instead of a concentrated ball, and it is on a far larger scale due to Killer Bee being completely transformed. However, even in his full form, he does not possess an invincible shroud like the Nine-Tails, so even with his immense size, powerful attacks such as Chidori Sharp Spear and Amaterasu will still be effective.

In part with his control over the Eight-Tails, Killer Bee can turn parts of his body into parts of the Eight-Tails body. For example, he can turn his chakra tails into a solid Eight-Tail tail.

Trivia

 * In chapter 471 of the manga, Killer Bee is seen with eight tails in a number of panels despite other characters saying he has seven. These extra tails appear and disappear without explanation.