: Well, I was wondering who Mazzarin was. He was an
: Avatara, I think but was he one of the nine? Was he
: killed by the Watcher?
Not one of the Nine during the Great War, no, but according so some sourced he founded the original Nine, which is synonymous with the Avatara.
: About the Watcher, the guide say that he is the 'second
: or third most powerful sorcerer in living memory'.
: Well, who is the other one(or two)?
Balor is the first, and the Deceiver is tied with the Watcher for second (one or the other might be more powerful, we're not sure).