Black Blade Basics
Source: Ultimate Magic, p. 47
A black blade is bonded to a particular magus, much like a familiar, but in more of a partnership than a master-servant relationship.
Intelligence: This is the intelligence score of the black blade. It starts at 10 and increases by 1 for every two levels of the bladebound magus (at 3rd level, 5th level, and so on).
Wisdom and Charisma: As the bladebound magus increases in level, so do the Wisdom and Charisma of the black blade. These abilities start at 6 and increase by 1 for every two levels of magus.
Ego: A black blade starts with an ego of 5, and that ego increases as the blade becomes more powerful, as per Table 1–3 below. In cases where a wielder and the black blade come into conflict, like any intelligent item, a black blade can attempt to exert its dominance using the rules on page 535 of the Core Rulebook. Due to its flexible and powerful nature, a black blade has a nonstandard ego progression.
Languages and Skills: A black blade starts with Common as a language. As the black blade increases in Intelligence, it manifests knowledge of languages and arcane lore. Upon reaching an Intelligence of 12, it gains a bonus language of the GM’s choice, and gains 1 rank in Knowledge (arcana). Each time the sword gains a bonus to Intelligence, it gains another language and another rank in Knowledge (arcana).
Senses: A black blade is aware of everything around it like a creature that can see and hear. It can be blinded and deafened as if it were a creature. It uses the saving throws of its magus, even if the magus is not currently wielding the black blade.
Black Blade Arcane Pool: A black blade has an arcane pool with a number of points equal to 1 + its Intelligence bonus.