Okay, this isn't exactly an Iron Man sequel per se, but in the likelihood that Black Widow gets her own spin off movie, does anybody else think Madam Masque would be the perfect villain for it?
You can mention her father trained her left her in charge of the Maggia a Mafia like organization with world wide pull, her gold mask can be explained as a gift from a lover of hers known only as Midas.
I'd have Natalia be sent on a mission by SHIELD to gather information on the Maggia and apprehend it's leader known to them only as Madam Masque. Along the way we'd learn of and see Masque's bio-duplicates and how paranoid Whitney Frost is. When Widow starts to get close to discovering the REAL Madam Masque, she'd be confronted by Masque's special enforcers, known as her Inner Guard. Eventually she'd find the real Madam Masque and and an epic smackdown would ensue with both weaponry and hand to hand combat. Widow winning, of course, but only by the skin of her teeth.
I haven't fully thought it all through yet, but wanted to get this out there.