The Blackstaff is literally a black wooden staff. It is similar in most ways to a normal wizard's implement, only where a normal focus would be carved with runes to focus the powers channeled through it, the Blackstaff is devoid of any markings.
Harry Dresden claims to have a distinct feeling that the Blackstaff appears to have a kind of consciousness all its own which is aware of its purpose (primarily, killing), and to want nothing less than to carry it out as swiftly as possible. Dresden also notes that it appears to attempt to exert some kind of control over its wielder, as black tendrils seem to crawl up the arm of the wielder and hurt him, before fading over time.
In the seriesEdit
Numerous times throughout the series, Harry Dresden and others claim that magic can only be used to perform acts that the user believed in. Once Dresden discovered his former mentor's actions as the Blackstaff, he was shocked by his capabilities to break the First Law of Magic despite his teaching Dresden the philosophy of magic previously mentioned. It seems plausible that the Blackstaff may be able to exert its own will in order to carry out actions that the wielder may not believe in.(reference needed)Jim Butcher has said that the Blackstaff protects the user from the backlash a warlock experiences when using black magic, the phenomenon of it "being easier to bend someone the more you yourself are bent." It may also allow a wizard to accomplish a GOAL he believes in without believing the magical method is just.(reference needed)