TV Guide's Michael Ausiello has some "Supernatural" casting news. Plus, we give you a rundown of what fans can expect in season three (warning: spoiler alert!).

According to Ask Ausiello at TVGuide.com, a "Buffy" alum is headed the Winchesters' way. The November 15th episode will feature Mercedes McNab, who played school-girl-turned-vampire Harmony on "Buffy" and "Angel." Word is that she'll be portraying a vampire on "Supernatural," too.

Back in July, series executive producer and creator Eric Kripke talked to Ausiello about season three. The addition of two new recurring female characters has been controversial, but Kripke, who has stated that he pays attention to fan websites and blogs, reassured viewers "we're not turning into One Tree Hill with monsters." The goal, he said, is to expand the Supernatural universe, emulating shows such as "The X-Files," which focused on the core partnership of Mulder and Scully, but had a rich array of supporting roles. Kripke added that in season three, "It's war. We're at war...we feel this is the most exciting season yet."

Jensen Ackles, who plays Dean Winchester, recently told The CW Source blog that Dean, who has one year to live after bargaining his soul to save his brother Sam's life, will be "having a lot of fun," while Sam will try to keep Dean focused on their mission. Jared Padalecki, who plays Sam Winchester, talked about "the darker side of Sam" hinted at in season two. Although he said that so far there's no sign of Sam going evil, this year "Sam will be a little quicker to pull the trigger." Because of the terms of the deal that saved Sam's life, the Winchesters can't weasel Dean out of his contract with a crossroads demon, or Sam will go back to being dead. "Sam is in this weird situation," said Padalecki. Sam wants to save his brother, but is frustrated because Dean "is acting like [he] doesn't want to live, like [he] doesn't care."

At this summer's Comic Con, Kripke said the season "opens up and escalates" the show's mythology as Sam and Dean hunt down all the demons that escaped from hell in the season two finale. The season opener, "The Magnificent Seven," involves seven demons who are personifications of the seven deadly sins. Fans can also look for the return of the legendary antique Colt revolver this season. As for the interaction between the brothers, "Dean is looking to get his hedonism game on as much as possible...Sam, there's a lot of static with that, because Sam is saying 'you're leaving me, you're abandoning me in a year.'"

"The love and loyalty that they show between each other will always be there," said Kripke. "It's always been a show about family."

The third season of "Supernatural" premieres October 4, 9ET/8CT on the CW.