Bruce Banner creates the MCU version of the intelligent Professor Hulk in Mexico, with funding and assistance from Tony Stark (Robert Downey Jr.). This doesn’t seem like a bad thing considering the Science Bros’ combined massive intellect. That is, until you remember that the dynamic duo has an abysmal track record when it comes to superhero experiments. Banner and Stark’s most notable scientific team-up before Professor Hulk is an artificial intelligence that becomes Marvel’s Avengers villain Ultron (James Spader) and nearly destroys the world in “Avengers: Age of Ultron.”
Imagine the pair tinkering away in Mexico with full knowledge of their Ultron failure while also coping with the mental anguish from Thanos’ victory in “Avengers: Infinity War,” and … well, let’s face it, there’s no way they wouldn’t include some fail-safes in case of a Hulk overload. A comics-style forced transformation to Banner when Hulk becomes too angry would be extremely on-brand, as would the unintended side effect of introducing a savage version of the meek scientist. A berserker Mark Ruffalo attempting to attack an enemy while in full Hulk rage mode sounds like a very MCU-style gag.
There’s also a legitimate storytelling reason for introducing a new weakness in the MCU Hulk. Traditionally, his only Achilles heel has been his own emotions. With the Professor Hulk mode combining the best of Banner and Hulk, he has no real reason to get angry or scared anymore. After all, he’s a super-smart scientist with a body strong enough to use the Infinity Gauntlet and survive. But superhero stories abhor perfection, and since Hulk likely hasn’t made his last appearance in the MCU, the franchise will need a way to nerf the guy before long.