Once they had agreed on a spar, Tobias began by summoning two items from a rippling portal created by his Kamui. The items were: a gray shakujo made from the same material comprising the infamous chakra receivers, and a double-edged sword whose blade was crafted from his own (shikotsumyaku) bone. He grasped the items with a firm grip and stepped forward while thrusting the sword, whose name was Mugen, toward his opponent.
The threatening maneuver activated an intricate Fuinjutsu embedded within Mugen's hilt that unsealed the uncountable number of shikotsumyaku blades stored within it, causing the blade to elongate with an exponentially-increasing velocity. To make matters worse for Shadow, Mugen took on an obsidian hue as he infused it with his Six Paths Power--not only boosting the speed of its expansion, durability and cutting power by a factor of 2, but imbuing it with the attractive power of his Rinnegan's Deva Path.
This attractive force would pull Shadow toward the weapon's point, increasing the odds of it puncturing his chest and exiting the other side. Tobias possessed unparalleled precision due to his sharingan and the cybernetic parts that he'd added to his eyes and visual cortex, and this showed in his deliberate positioning of the blade so that it would avoid the man's heart while still puncturing his left rib.