Yata Mirror

The Yata Mirror was carried by Itachi's Susanoo in it's left hand. It is considered one of the three sacred treasures and is endowed with all nature transformations, it can change its own characteristics depending on the characteristics of the attack it receives, making the technique ineffective. Zetsu claimed that this, combined with the Sword of Totsuka held in its right hand, essentially made Susanoo invincible.