Transformation: Adamantine Staff

Monkey King Enma's transformation technique, which is characterised by the hardness of diamond and its at-will extendibility, the Adamantine Staff is the Third Hokage's "weapon of choice", so to speak and with it in hand he's made it through a world of war for an extended period of time.

When Enma is transformed into the Adamantine Staff, it is possible for him to attack on his own free will, with his claws and fangs adding an element of surprise and irregularity. Forged in the fire of battle, its at-will transformation-based attack and defence go beyond the scope of proficiency, to attain the realm of shinobi "godhood". The main method of attack consists in strikes and thrusts that take advantage of its ability to extend.

The hardness of diamond also translates into destructive power. Despite its hardness, Enma stated that he could still suffer damage from weapons such as the Kusanagi wielded by Orochimaru.

Trivia

 * The concept of an extendible staff is based on the story of Sun Wukong and his Ruyi Jingu Bang.
 * A nyoi, which can be translated as priest's staff but literally means as one (a person) wishes, is an auspicious decorative object associated with Chinese Buddhist rituals. It was made from bone or jade, with a head shaped either as a cloud or as a lingzhi mushroom and had a slightly curved handle, but the production and use of these objects declined after the Tang Dynasty.
 * Vajra, which is in Japanese, is a mythical material that is said to be able to cut through any substance, but cannot be cut itself.