Ibuse

is a venomous salamander and Hanzō's signature summon. It was large enough for its summoner to stand on top of its head and when battling alongside Ibuse, Hanzō was powerful enough to fight, and eventually overpower all three of the Sannin.

Background
Ibuse took part in Hanzō's fight with Jiraiya, Orochimaru and Tsunade. It has also fought numerous times against Chiyo.

Abilities
Ibuse is able to release a Poison Mist from its mouth, which is capable of making the entirety of a victim's body numb just moments after inhalation and may eventually prove fatal, although these effects can be counteracted with the correct antidote. The poison must first be generated and then stored for a total of five minutes within Ibuse's body before it can be expelled again.

Ibuse is capable of concealing itself and navigating underground. It can then resurface beneath Hanzō's enemies and swallow them, trapping them in its mouth until they have succumbed to the fatal effects of the poison.

Shinobi World War Arc
While pursuing the Surprise Attack Division, Hanzō summoned Ibuse, who immediately exhaled a large quantity of poison in order to immobilise the fleeing shinobi. Hanzō then leaped off of Ibuse to finish them off but they are saved by a group of samurai. Chiyo then divulged to Kankurō and the samurai that Ibuse's poison needed at least five minutes to replenish. Because of this, Hanzō ordered it to hide underground. It later emerged beneath Mifune, swallowing him in an attempt to kill the samurai, however, Mifune slashed through Ibuse's head and escaped.

Trivia

 * Despite initially be portrayed as being green in colour, during it's later appearance in the anime it is depicted as being a brown colour.