Surely, HQ won't be the only villain we face in this chapter. I am certain another villain will be teaming up with her for the chance to take Batman and Robin down, or at least take advantage of the situation to do so. Someone like Killer Croc or Bane.
The Mandarin should be the main villain, but if they aren't going to go with alien technology, even though it was established in Thor and the Avengers, make the rings' power more symbolic, like the keys to a doomsday weapon.
After that, Iron Man still needs an armored baddie to match his power and bring a challenge, like Titanium Man.