WARNING: The following contains spoilers for The Immortal Hulk #39 by Al Ewing, Joe Bennett, Ruy Jose, Belardino Brabo, Paul Mounts, & VC's Cory Petit, on sale now
The Hulk hasn't always been one of the brightest Marvel heroes, which has allowed villainous figures over the years to figure out how to outsmart or trick the Jade Giant. But now, the Avenger's recent mistake just cost him a dear ally and maybe far more.
In The Immortal Hulk #39, the Savage Hulk was just tricked into a very costly mistake that might have doomed not just Bruce Banner, the entire Marvel Universe and maybe even the multiverse.
After finally escaping capture within Hulk's mind, the Devil Hulk proceeds to beat the Leader down. Despite having taken over the form of the World-Breaker Hulk, the Leader has nothing to counter Devil Hulk's beating. All of his attempts to trick the Devil Hulk or force his sympathies fail, the Leader soon moves in for the kill. But one of those gambits -- taking the form of Brian Banner, Bruce's father -- is actually enough to set off one of the other Hulks: the child-like Savage Hulk.
The Savage Hulk, hoping to end the fight and revealing that it never wanted to kill anyone, tries to hold the Devil Hulk back. The Devil Hulk is more heartbroken than anything else, having only wanted to protect Bruce and -- by extension -- the Hulk. But this gives the Leader just the opening he needs. The villain is able to unleash his true form and rip the Devil Hulk apart, cutting off his head and pull out his heart. This allows the Leader to then carry a struggling Bruce out of his own mind and into the Below-Place, where he's quickly morphed into what could become the ultimate form of the One-Below-All.
This might have been the first step towards the end of all creation in the Marvel multiverse. The One-Below-All has been seeking out a physical form so it could break through the core Marvel Universe, specifically Bruce Banner as he's been so exposed to Gamma Energy that he makes for the perfect vessel. All of its schemes and machinations have been towards this goal, forcing Hulk to embrace the Devil Hulk in a bid to stay ahead of his enemies. Although the beast is a cruel and clever version of the Hulk, the Devil Hulk also dedicated itself to protecting Banner under any and all circumstances. But now, it looks like that the Devil Hulk is gone, ripped apart by the Leader, and Bruce has been stolen away so he can give the One-Below-All his ultimate form.
This is the being known as the true World-Breaker, who will ravage the universe even after all things have died and been replaced with a new universe. It could even grow powerful enough to traverse through the multiverse, destroying entire realities until it is the only thing left in creation. This has been the dark fate Immortal Hulk has been building to, and it's heartbreaking that the potential key moment wasn't that the Leader won -- but that the Hulk failed. The Savage Hulk and Joe Fixit are still within the body of the Hulk, but that body is being held by Puck and Gamma Flight, which keeps them out of the fight until it's too late. The pair better find a way out, or the Savage Hulk's mistake might have just cost the lives of every single being in the Marvel Multiverse.