Isobu

The Three-Tailed Beast is a gigantic, turtle-like demon that Akatsuki assigns Tobi (with the help of Deidara) to capture. What abilities this creature possesses remains unclear, as it did little to actually attack the two in its short appearance. It is clearly quite fast despite its size, as evidenced by its ability to keep up with Tobi, who was running on the water at the time. With the demon turtle distracted, Deidara molded an explosive clay fish in an attempt to capture it. It's unclear if this marked the end of the battle, as the remainder of the battle goes unseen. As the two towed the Tailed Beast to the Akatsuki lair after the battle, Tobi gloated of bringing the Three-Tails down with his special jutsu, but Deidara thought otherwise. It is later sealed in the sealing statue.
 * Name:
 * Creature Type: Turtle-like creature
 * Host: None
 * Unique traits: Unknown
 * Status: Captured, and sealed by the Akatsuki.

Unlike the other Tailed Beasts seen this far, the Three-Tails lacked a host. According to Deidara, lacking a host made the demon turtle weaker because it wasn't intelligent enough to control its own strength.