Bruce Banner's most physically powerful heroes in Marvel lore, so when they get together, it's guaranteed that the results will be explosive. However, the first time that Venom bonded to Hulk, he enhanced the Green Goliath's strength in a way literally no-one was expecting.
The Hulk has a long history with Venom, mostly trading punches with the Jade Giant. However, Bruce Banner was also there for the symbiote's origin during 1984's Secret Wars, back when Spider-Man gave it a new home, believing it was a fabricated costume. Since then, Hulk has fought and - on a few rare occasions - bonded with the alien, combining their powers.
Usually, this results in a super-strong Venom with gigantic teeth and the ability to shift its symbiote matter into new weapons. However, when Hulk and Venom first combined, the symbiote did something far more creative with Hulk's might...

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Venom Combined the Powers of Spider-Man, Hulk and Thor
The Symbiote United Marvel's Strongest Powerhouses in One Body
In 1989's What If...? #4 (by Danny Fingeroth, Mark Bagley, Keith Williams, Tom Vincent and Ken Lopez), fans find out the answer to the question 'What If the Alien Costume Had Possessed Spider-Man?' The story breaks from Marvel Comics continuity when Peter Parker visits the Fantastic Four with questions about the symbiote. In this timeline, Reed is busy, and Peter moves on, keeping the suit despite his misgivings. The symbiote quickly drains Peter of his vitality, leaving him desiccated and near death.
The Avengers confront this new version of Venom, who quickly takes control of the Hulk, whose dim-witted mind is easily overcome. Venom then flees, while Peter tragically dies without the symbiote. When the Avengers pursue Venom, the symbiote tells Thor that it has bonded totally with Bruce Banner and has found a way to cure him - siphoning off his gamma radiation so that he never becomes the raging monster again. It also pretends to feel guilty about killing Peter, insisting it never wants to kill again - a claim Thor refuses to take at face value.

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The new Venom Hulk fights Thor, then switches to the Thunder God, possessing him while he's stunned. It's here Venom reveals the dark truth of its spree so far - having consumed its hosts, it has permanently taken their powers. Now in control of Thor, it has all the powers of the Thunder God, Hulk and Spider-Man, making it almost impossible to defeat or destroy.
Venom's ultimate form has every superpower ever included in Marvel lore, becoming the ultimate embodiment of biological life.
Venom Can Co-Exist With His Hosts, But He's Also Capable of Draining Their Powers
The Symbiote Easily Became the Strongest One of All
While heroes like Captain Marvel and Human Torch try to defeat the new Venom Thor amalgam, he sends each of them flying, and is only defeated when Black Bolt combines his powers with Reed Richards' tech, with Black Cat using stolen weaponry to kill the alien once it's separated from Thor, gaining vengeance for Peter. While Venom has since learned to work in concert with its hosts, it was originally a predatory organism that consumed its 'other' by keeping them in a high-adrenaline state. What If...? revealed that by doing this, Venom can keep the powers of superhuman hosts, combining the immense strength of Hulk, Thor and Spider-Man - three of the physically strongest Avengers.... But what if it didn't stop there?
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Codex Venom Has the Powers of Every Marvel Superhuman
As powerful as the original Venom Hulk is, the symbiote topped that form in Venom: The End, by Adam Warren and Chamba. The story takes place in a far future where Venom is the last form of biological life, waging war against a species of advanced AI descended from Tony Stark's technology. Venom is able to access the power of all his past hosts, using the time travel of various X-Men mutants to travel back through the timeline and make with every living superhuman, granting the symbiote every superpower in Marvel history.

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Venom has merged with many villains throughout the Marvel Universe, giving them shocking redesigns that made them more terrifying than ever before.
While this makes Codex Venom more powerful than even the gods, it still only makes the symbiote a match for the Starkware AIs, who can alter reality due to cracking the cosmic mathematics underpinning reality. Codex Venom has the powers of Multiple Man, Storm, Elixir, Deadpool and Magik, creating an endless army of time-warping, weather-controlling, near-unkillable Venom clones who all in the battle, which lasts for over a trillion years.
Ultimately, even Codex Venom can't beat the AI beings, and the symbiote uses its amazing abilities to rebirth an entire universe, populated by every living thing in its codex. This pocket universe is ultimately preserved as a curio by the AI gods, turning Venom into the final protector of biological life, with a single pocket reality being all that remains in a multiverse otherwise ruled by AI.
Even in current comics, Venom has only begun to explore the full potential of its powers. While the symbiote naturally accesses the powers of its host, it has a far more sophisticated ability to steal and replicate countless superpowers - but generally only at the cost of its host's life. Marvel's original Venom Hulk showed what the symbiote was capable of, uniting the powers of Hulk, Thor and Spider-Man in a single body - but even that was only a glimpse at what Venom could one day become.
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The Hulk, a Marvel Comics superhero created by Stan Lee and Jack Kirby, is physicist Bruce Banner transformed by gamma radiation. He morphs into a giant, green-skinned creature of immense strength and invulnerability when angered. Struggling with his transformations, Hulk allies with other heroes, battling villains while balancing his intellect with uncontrollable rage, making him a central figure in Marvel's universe.
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Venom is a symbiotic alien entity bonded with various human hosts, notably Eddie Brock and later Flash Thompson. It grants superhuman strength, agility, and a shape-shifting black costume. Initially a Spider-Man villain due to its origins, Venom evolved into an antihero, battling both villains and his own dark impulses. The character embodies themes of duality and redemption within the Marvel Universe.