A recent discussion prompted this out of my memory, one of those ideas I know I'll never get to use, so...my idea for 'Hulk 2'. It draws freely on comic elements, in particular those of Peter David's run on the Hulk (in fact stealing one scene outright, but since it is an adaptation, I think that'd probably be alright assuming he was credited. Which he is, here.)
Basically, it picks up where the first Hulk movie left off--Banner's on the run, hiding out in some Third World country and trying not to get "angry". The US government suspects they might know where he is, but they don't have extradition treaties with that country, so they hire, through back-channels, an ex-KGB mercenary named Emil Blonsky to go retrieve Bruce Banner, dead or alive. He's briefed on the Hulk situation, but is very confident (over-confident, even) that he can take care of the situation without problems.
Meanwhile, Bruce is approached by a man calling himself "The Leader". He's an insurance salesman who was contaminated by waste products from Bruce's gamma experiments, and his intelligence has been increased a hundred-fold; however, without the stabilizing nanites and Bruce's genetic alterations, the gamma radiation is killing him. He's super-intelligent, but doesn't have Bruce's background in the field. He offers Bruce a deal; if Bruce stabilizes his condition, he can a) take care of Blonsky, whose pursuit is news to Banner, and b) stabilize Bruce's condition. (The Leader also implies that if Bruce doesn't stabilize his condition, he has it in him to sic Blonsky on him as a last act.) Reluctantly, Bruce agrees.
The two begin working together--Banner is the expert in the field, but the Leader's natural intelligence allows him to quickly outstrip Bruce's knowledge. While they're working, the Leader displays other, disturbing aspects of his power--he can use the power of his mind to control others with a form of hypnosis. Banner wonders why the Leader didn't just control him, but the answer is simple--he can't implant suggestions into another gamma-irradiated person. Finally, the process succeeds and the Leader is stable. Now, the same process can be used on Bruce...
...but Bruce doesn't get time to test it right away, as Blonsky makes his move, kidnapping Betty and forcing Bruce to come after her. Blonsky thinks he's outplayed Banner with this trick, forcing Bruce to drug himself rather than risk Blonsky hurting his girlfriend, but Blonsky hasn't reckoned with Bruce's new ally. The Leader helps Bruce defeat Blonsky and rescue Betty, taking her back to his base for "safe-keeping." Blonsky's fate remains a mystery...for now.
With that out of the way, Bruce is free to try his cure......but Bruce discovers too late that the Leader double-crossed him. The process doesn't stabilize Bruce Banner, it stabilizes the Hulk, creating a new creature not as smart as Banner, not as strong as the Hulk, but with many of the properties of both. This new, grey Hulk is also totally amoral, and quickly agrees to help the Leader boost his mind-control powers a thousand-fold and take over the world's governments.
An appalled Betty tries to get through to the Hulk as they work on the device, but the Hulk is unswayed and steals the necessary parts from the US military in a major action sequence. The Leader assembles the device and activates it, enthralling not just the world's leaders but every human being on the face of the planet, save the Hulk and himself. The Hulk is actually fine with this--until he finds out that Betty, too, is now a mindless slave of the Leader, and that the Leader plans to use her as nothing more than a "brood mare" of his new humanity. With that, the alliance is off and the fight is on--despite his avowed lack of morality and conscience, he still deep down loves Betty Ross.
The Leader is more than a little irked, since he can't control the Hulk. He can't implant suggestions into the mind of any gamma-powered being. Luckily, he explains as Blonsky bursts into the room, he can implant suggestions into someone and then transform them. Blonsky turns into a larger, uglier, scalier, mutated Hulkish thing that the Leader dubs, "My own personal Abomination", which then proceeds to stomp nine kinds of hell out of the weaker, grey Hulk.
The Hulk fights valiantly, but the Abomination gets him into a choke-hold. As his brain begins to die from lack of oxygen, we zoom through his eye to his mental state, and see him start to lose his hold on the mental "cages" he's trapped Banner and the green Hulk in. The green Hulk breaks free and the two of them fight, the grey Hulk refusing to relinquish the body he's fought so hard to attain, even if he dies in it. Their battle is inconclusive, finally ending in the two of them strangling each other to death even as the Abomination strangles his physical body...
...and then Banner steps up to the pair. He says, "That's enough. This stops now. I'm stopping it. Because you might be stronger out there, but in here?" BAM! One punch and the grey Hulk drops. "Banner is strongest one there is!" He turns to the green Hulk. "Go. Save Betty."
...and we zoom back out through the eyes as they change from grey to green, as the Hulk grows more massive, stronger, greener, breaks the Abomination's hold, and Round Two begins. The Abomination just isn't a match for the stronger green Hulk, and their conflict destroys the lab and the Leader's equipment. The Hulk breaks out with Betty as the lab is engulfed with fiery explosions, seemingly killing both the Leader and the Abomination.
After a time, the Hulk reverts to Banner. He explains to Betty that the changes the Leader made further fragmented his mind and body. What was a struggle between himself and the Hulk is now an uneasy three-way war between himself and two Hulks that hate each other, him, and probably everyone else...and it's not safe to be around her, or anyone. With that, he turns and heads off into the night, leaving Betty to wonder when she and Bruce will ever be free of the curse of the Hulk.