Wood Release: Great Forest Technique

A technique that changes one's own arm into big trees. Using chakra, the tissues are transformed into trees at the cellular level. Then, by activating the trees, stimulating them to grow rapidly, they lengthen at high speed and fork into many branches. It is possible to capture the enemy with these branches and at the same time, if one changes the ends into sharp stakes, turn them into countless, sharp, spear-like piercing weapons.

Yamato also used this technique to infiltrate Orochimaru's hideout. After finding a small crack in the wall, the wood squeezed into the hole and grew into a square shape which increase the size of the hole so that he and his team could pass through.

Trivia

 * In an anime cutscene of Tobi's storyline in Naruto Shippūden: Ultimate Ninja Storm Generations, Hashirama Senju uses this technique against Madara Uchiha to place him in a position so Hashirama could apply the Contract Seal.