Killer B's Jinchūriki Forms

Kirābī 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 only displayed two forms. Unlike Naruto and Gaara, he seems to have 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.

Three-Tailed Transformation
When need be, Kirābī will tap into the Eight-Tails’ chakra and generate a demon cloak similar in appearance to Naruto’s One-Tailed Transformation (and onwards).

In this form, his incisors and nails grow long and sharp and Kirābī is covered in a boiling chakra shield, that takes the shape of his Tailed Beast by forming three tentacle-like tails on his behind, and paws of chakra around his hands. However, instead of just creating fox-like ears like Naruto's demon fox cloak, his chakra cloak forms a pair of bull-like horns. Due to Kirābī's great control of the Eight-Tails, this transformation can be done instantly.

In this form, he has increased strength and speed, which Sasuke could barely keep up with using his Sharingan. Additionally, the bull horns of the shroud can be used for powerful piercing attacks, at one point blowing away Sasuke's entire neck and chest. However, unlike Naruto's one-tail transformation, Kirābī's attacks in this form are straightforward and can be read with the Sharingan.

Full Eight-Tailed Transformation
While fighting Sasuke and his team, Kirābī managed to wound Sasuke long enough to transform into the Eight-Tails' full form.

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 black 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 Kirābī being completely transformed. However, even in his full form, he does not possess an invincible shroud like the demon fox, so even with his immense size, powerful attacks such as Chidori and Amaterasu will still be effective, the latter defeating him in this form, though it was revealed that Kirābī was only pretending so that he could escape his village.