She is Mata Hari. She is Morgana le Fey. She is every Film Noir vixen.
There is no Homme Fatale. The closest to that ideal is The Seducer, but The Seducer wants to seduce the Hero’s One True Love and not The Hero.
Her goal is to seduce and betray the Hero.
She may also seduce the Villain, but she won’t ever love the Villain (not truly).
She is feminine. She misuses her femininity, but she does not employ masculine means to achieve her goals.
She does not see herself as evil. Deep inside, she’s motivated by her sense of frailty. She is afraid of men and uses her womanhood against them. She also wants to be loved but is not willing to admit that to herself.
Sex is her weapon.
She is both sexual and carnal. She likes sex, both for its pleasure and because of its power.
Only the Hero can make her fall in love.
Only the Hero can give her an orgasm (although she does know how to fake it).
Unlike the One True Love, she’ll have sex on screen (or on page, as the case may be).
Sex is never tender (even with the Hero) and is often kinky.
If she ever falls in love, she will die. The Hero will avenge her, of course (although she won’t ever be the axis of his vengeance) but she will remain dead all the same.
Her death validates her deepest fear: vulnerability is fatal; however, the love she feels serves to redeem her, especially if she sacrifices her life for the Hero.
She can never become the One True Love. She can sometimes dupe a Hero into believing that she is, but she ain’t.
She is beautiful. This goes without saying.
She is comfortable with knives and poison. She’ll use a gun if she has to, but it’s really a horrible lapse of style when that happens.
She is vain. She can not stand the thought of other people being more attractive, and she is repulsed by True Beauty.
She is doomed. The Femme Fatale does not survive to the end of the story. Half the time, she won’t even reach the 75% mark.
The Femme Fatale is not spiritual. If she believes in God, she doesn't give him much thought.