Warning: This article contains spoilers for the post-credit scene of Shang-Chi and the Legend of the Ten Rings.
It was confirmed last year that Mark Ruffalo would be returning as Bruce Banner in She-Hulk, alongside Tim Roth's Abomination. The latter of whom made an appearance in Shang-Chi and the Legend of the Ten Rings fighting Wong of all characters.
As anyone who has seen the film should know, Abomination wasn't the only surprise cameo. In the first post-credit scene for Shang-Chi, Brie Larson's Captain Marvel and Ruffalo's Bruce Banner appear speaking to Shang-Chi about the Ten Rings and their origins.
The biggest shock of this post-credit scene was seeing the return of puny Banner. As far as the audience was aware, it was seemingly implied that Banner's transformation into "Smart Hulk" was permanent in Avengers: Endgame.
So, how has Banner returned to normal? One possible explanation might involve the curious-looking armband fastened on Banner's left arm in the post-credit scene.
The Answer Is in the Armband
One odd accessory that Banner was seen wearing in the stinger is an armband on his left arm. Upon closer expectation, it even has a small glowing green screen on it too. He never wore anything similar in his previous appearance in Avengers: Endgame.
By itself, it seems like nothing more than a scientific device for one of the smartest people on Earth. However, coupled with Banner's sudden reduction in size and knowledge from the comics, it could actually be exactly what has allowed him to return to his smaller stature.
There was a point in the comics that Bruce Banner actually stopped being the Hulk due to all of his Gamma radiation being put into someone else. That someone else in the comics was teenage genius Amadeus Cho, whose mother appeared in Avengers: Age of Ultron.
When Banner absorbs too much radiation, leading him to nearly explode and kill millions, Cho siphons Banner's gamma into himself instead and becomes the new Hulk. To do this, Cho used nanobots based on technology created by Samuel Sterns a.k.a the Leader, called Sternbots.
It is what allowed Cho to alter the structure of his cells to contain and use Banner's gamma energy. Using a device strapped to his arm—not dissimilar to the one Banner has in the post-credit scene—Cho could manually control his transformation into the Hulk using these Sternbots.
It's possible that this could ultimately end up being the explanation in the end for Banner, but why and how is another question that will likely be answered in She-Hulk.
The Incredible Hulk No More?
Fans have already seen that Mark Ruffalo will be donning a motion-capture suit once more, signifying that Hulk will be making a return in She-Hulk, but for how long? It was confirmed that Abomination would be returning too, and he's also stuck permanently in that monstrous form, at least in the comics.
Having three CGI-intense characters with She-Hulk, Hulk, and Abomination at once might be too expensive for even a show funded by Disney. It could be that Bruce has continued to experiment on himself and found a way to revert to his normal self again, while also being a way of saving the budget for Tatiana Maslany's Jennifer Walters.
Also, despite this device originating with Cho, it doesn't seem like there have been any reports or rumors that he's been cast in She-Hulk. So it's unlikely that fans will see the gamma-irradiated torch passed down like in the comics in She-Hulk.
Fans will find out for sure what's up with Bruce Banner when they see him again in She-Hulk on Disney+ in 2022.