Episode Title:
Kakashi Enlightened!.
Episode Description:
Kakashi destroys Deidara's arm with Mangekyo Sharingan: Kamui. After Naruto beheads the clay bird with his Rasengan, he sees the dead and lifeless body of Gaara. This causes Naruto to angrily attack Deidara and accidentally uses his Nine-Tails chakra, causing him to transform into the beast with two tails.
