-vampire mobsters
-run by three brothers; aro, marcus, and caius
-people who do the dirty work: jane, alec, felix...
-italian vampires

Mercury retrograde is the act of taking a shit whilst mooning one or more human beings. Your day can typically being going well, according to your horoscope, until you are forced into witnessing Mercury retrograde. Performing Mercury retrograde will often speed the astrological cycle forward for the individual performing the Mercury retrograde, bringing about happy and fruitful times to come.

something you threaten people with.

The Volturi are a group of ancient italian vampires that protect vampire law. In other words make sure the existence of vampires stay secret. The Volturi Coven includes Aro, Caius, Marcus, Sulpicia, and Athenodora. And Didyme used to but Aro killed her because he was too power hungry to let Marcus and her leave the Volturi. There's also The Volturi Guard. That consists of Alec, Jane, Felix, Demetri, Chelsea, Renata (partial). Basically they do all the REAL work. Aro, Marcus, and Caius aren't kick-ass enough to do much so they have others to do their bidding. In short Alec, Jane, Felix, and Demetri do pretty much everything and sometimes consult with Aro. In modern times (via Breaking Dawn) Aro has become tired of Plan A: Keep the existence of vampires a secret to Plan B: Take over the vampire world in power hungry in greedy ways.