Warning: If it's possible to spoil movies that are 10-20+ years old, this post may contain spoilers by revealing the identity of killers who were involved in twist endings.
1. Baby Firefly // House of 1000 Corpses (2003), The Devil's Rejects (2005)
Baby Firefly (Sheri Moon Zombie) made her mark on the horror world with her comedic, almost childlike demeanor in Rob Zombie's House of 1000 Corpses. However, viewers quickly learned that Baby had a dark side hiding behind that sweet smile, and that she was just as demented as her psychopathic brother, Otis (Bill Mosely) and the rest of the Firefly clan. By the time The Devil's Rejects was released, Baby seemed to have matured quite a bit -- but she certainly hadn't lost her knack for killing and had a sadistic streak that could put both her brother and her father, Captain Spaulding (Sid Haig) to shame.
Jennifer // Jennifer's Body (2009)
Jennifer (Megan Fox) always had a bit of an insatiable appetite for men, but the shit really hit the fan when the nerdy dude from the OC tried sacrificing her to Satan and she ended up possessed by a Succubus. Jennifer used her good looks and charm to lure horny teenage boys to their deaths, and used their entrails as a sort of afternoon snack/fountain of youth combo that would surely make Countess Elizabeth Bathory proud.
Marie // Haute Tension (2003)
Oh Marie (Cécile De France). For a significant portion of this French flick she probably really thought she was chasing down a madman in hopes of saving her best friend. Well, it turns out dear Marie was really the bad guy all along, and Haute Tension provided viewers with one of the few successful multiple personality copout endings in horror cinema history.
Tiffany // Bride of Chucky (1998)
Everyone deserves a little love, and dolls possessed by deceased serial killers are no exception, right? 1998 was the year Chucky (Brad Dourif) finally decided to settle down with the gal of his dreams, Tiffany (Jennifer Tilly). In both doll and human form, Tiffany was a match made in Heaven (erm..hell?) for Chucky, and she helped him carry out some of the most comical and creative kills in the Child's Play franchise.
Annie Wilkes // Misery (1990)
Annie Wilkes (Kathy Bates) is a classic villainess no list like this would be complete without. She's that sweet lady next door who loves nothing more than to immerse herself in a good book at the end of the day -- well, almost nothing. In her free time, she enjoys holding her favorite authors hostage and breaking their legs with sledgehammers when they don't do her bidding.
Mary Mason // American Mary (2012)
I was a bit hesitant to include Mary (Katherine Isabelle) on this list, because in truth, I don't really see her as a villain. Buuuut she is from a horror film and she does kill people, so whatever, close enough. Mary stands out from the traditional tropey ladies of the rape/revenge (gross) sub-genre, because she's a woman who refuses to be defined by the tragedy that's befallen her and her story begins after she's exacted her revenge instead of ending once the asshole is dead .
Brenda // Urban Legend (1998)
Okay admit it: you totally thought Robert Englund or Jared Leto would end up being the killer the first time you watched Urban Legend. I know I did. But Brenda (Rebecca Gayheart) had a bit of an evil streak hiding behind those bright green eyes, and came out to surprise audiences everywhere as the true axe-wielding murderess intent on stealing Alicia Witt's kidneys. And it was glorious.
May Canady // May (2002)
May (Angela Bettis) is another killer I feel a bit bad for classifying as a "villain," but a quick trip to the IMDB boards for May reveals that plenty of people see her as the spawn of Satan himself. Personally, I see her as a very sick and lonely lady who snapped, but I'll let you make up your own minds. May really wanted a friend. Like, reallyyyyy bad. So bad, she decided to make one....using parts she hacked from the bodies of people she once thought were her friends after they let her down one too many times.
Asami Yamazaki // Audition (1999)
Just when you thought girls crawling out of television sets were the most terrifying thing to hail from Japan, Asami (Eihi Shiina) showed up wielding piano wire, acupuncture needles and a deep-seated love of torturing lonely widowers.
Lola // The Loved Ones (2009)
Lola (Robin McLeavy) should be a lesson to you all about why you shouldn't say "no" when the weird girl at school asks you to the Prom -- she will kidnap you, inject your vocal chords with bleach and add you to a collection of lobotomized men she keeps hidden in her basement. Seriously. Just buy the girl a nice corsage and go to the dance.
And for the hell of it.... a few Honorable Mentions
Rhoda Penmark // The Bad Seed (1959)
Rhoda (Patty McCormack) was one of the first evil children in cinematic history. With her pretty dresses, sweet smile and ribboned braids, Rhoda successfully hid her true nature from her friends and family for years -- well, until she drowned one of her classmates and lit her building's maintenance man on fire, that is.
Pamela Voorhees // Friday the 13th (1980)
Mrs. Pamela Voorhees (Betsey Palmer) shocked audiences around the world when she was revealed as the killer in Friday the 13th. Before being replaced in the subsequent sequels by a nonsensical version of her deceased son, Pamela spent her downtime exacting revenge on lusty camp counselors for the death of her little boy, Jason.
I've worked really hard to put together a lot of content for you guys this month, and this is just the first of many great things to come in the next few weeks :) Definitely keep checking back for lots more posts to get you geared up and ready for Halloween!