I had the greatest idea for a sequel today, and it's also a lot like a crossover.
And there are also spoilers.
So, the movie begins with Bruce Banner traveling across the world, now content with his inner Hulk, and while not able to fully contain it, he can limit its actions and objectives. And in other news, Betty and Ross are trying to come closer as father and daughter, while Tony Stark and Nick Fury begin adding more links to the US army, starting with Thunderbolt Ross. Betty is worried that her father may be after Bruce again, so she goes out to find him. And who's tracking her? No one else but dear ol' daddy.
During this, we see shadows of a man going into a bar in a distant country. He asks for volunteers to be apart of his new army. Someone tells him that the man's nuts, and is quickly on the floor dead in the wink of an eye. In fear, the rest agree, and mention other places to find followers.
We go back to Bruce, who is warned of Betty's coming by her, but soon finds on satellite that SHIELD and the US army appear to be following her.
While preparing a plan to get Betty without being seen by everyone else, Bruce notices a bunch of men in odd uniforms heading into an empty warehouse. Of course, the doctor goes to investigate. Once he sneaks in, he hears a familiar voice. "Banner!" he shouts. Coming down on a hovering platform is none other than Samuel Sterns, now green and with the largest brain around. Calling himself the Leader, Sam shows his former associate a device that can manipulate gamma radiation, mainly Bruce's. Ah, but Bruce now has better Hulk control, and speeds up his blood pressure, initiating the transformation sequence. But the Leader's device is designed for manipulation on Banner pre-transformed, let alone during the transformation sequence.
But finally, the transformation is over, and out comes the Hulk. Oh, but not the green Hulk. We're talking something much bigger, and much meaner. Ladies and gents, meet the Gray Hulk. The Gray Hulk then begins to rip apart and destroy everything in sight. In a last ditch effort, the Leader takes the surviving men with him in an escape pod, with a brand new plan.
Gray Hulk forgets about Betty and decides to do whatever he wants, including scaring people and destroying towns he doesn't like.
The army then picks up Betty against her will, and go to grab this nastier Hulk. When meeting up with the Gray Hulk, the beast ignores Betty(breaking her heart), and tells General Ross to back off. Of course, he refuses, and the army fights. They lose, and Tony Stark comes in as Iron Man. His Mach III armor is trashed, and Tony retreats with the army.
This is where we go to SHIELD headquarters, and the Leader breaks in with his posse. Sterns then looks for the prisoner's wing, where we get all sorts of villain cameos(any you wish, really). The plan? Free the Abomination! Blonsky agrees to work with the Leader, as long as he gets his rematch with the Hulk.
Now, Betty works with Stark and SHIELD's top scientists to find a way to reconfigure the Hulk back to his old self. They find a way, but it must be drunk. So what is planned for this mission? Tony Stark's newest creation: The Hulkbuster Armor.
We then get an epic battle between the Hulkbuster Iron Man and the Gray Hulk. Once the Hulkbuster Armor is almost completely destroyed, Tony manages to make Gray Hulk drink the serum, and Banner's back to his old self. And right at that moment, Leader's hovercraft appears, takes everyone hostage, and the Abomination finishes off the damaged Hulkbuster Armor. Leader tells Bruce where they will be, and that he has 24 hours to save everyone as the Hulk, or else.
Then the final battle between the Hulk, Abomination, and Leader's high tech army begins!