What the Immortal Hulk has is technically called “Retroactive Immortality”. He can be killed, but he will come back to life following his death. This is not exclusive to Hulk, if Banner is killed, he will be brought back when Hulk resurrects as well.
Bizarro is Superman's infamous and sometimes lovable clone/doppelganger opposite gone bad who possesses near-identical powers to the Man of Steel. He has more than enough strength to match the Immortal Hulk's and the addition of his freeze vision and fire breath would be enough to secure a victory.
During "No Surrender," Banner realized Hulk's immortality. Considering the number of times the Hulk has been resurrected, it's no coincidence that death never sticks for the behemoth. Indeed, the Immortal Hulk reveals that when Banner first detonated his gamma bomb, he incidentally opened the Green Door.
The Hulk's one weakness has been cosmic radiation. While the power of gamma has seemed unstoppable in the past, cosmic radiation has been the Hulk's Kryptonite. Henry Gyrich exploited this by siccing the U-Foes on the Hulk, with X-Ray dousing the Hulk with cosmic radiation and killing him yet again.
Before he can defeat him, the Immortal Hulk is stopped by the Savage Hulk, who is being emotionally manipulated by the Leader. The Immortal Hulk is beheaded by a monstrous Leader and his heart is ripped out. His corpse, alongside Banner, is taken to the Below-Place by the Leader.
Considering the Hulk is powerful enough to beat up a God it shouldn't come as a surprise that when the Hulk finally corners the God of Sleep, he kills him without breaking a sweat. Related: The Hulk is Secretly A Mathematical Genius (Seriously).
His new gamma burst can destroy an entire planet in an instant, if this wasn't enough Immortal Hulk can sense liars and drain Gamma from other Gamma-based life forms. This combined with the Hulk's other powers makes him one of the most powerful Hulks to date.
Putting it all together, Thor can win against the Hulk, even if he can't kill the Jade Giant. Hulk is practically immortal and has unlimited reserves of strength and stamina, so he can keep fighting forever. Thor's endurance, while godly, is not limitless, so he will eventually lose a prolonged battle.
Can the immortal Hulk kill Thanos? No, the Immortal Hulk, just like every other incarnation of Hulk before him, would fall before the power of the Mad Titan.
No matter how mad the Hulk gets, or what form he is in, it is just not possible for him to kill Manhattan, whereas Manhattan can take his molecular structure apart atom by atom.
In Immortal Hulk #39 by Al Ewing and Joe Bennett, Hulk travels to the Below-Place where Bruce Banner is ripped from his body by the One Below All. Not only that, but the abuse Hulk's body suffers while in this hellish realm sucks him dry of nearly every bit of gamma energy flowing through his veins.
Ewing says that the idea was born from the fact that the Hulk has been resurrected so many times in the past. He also explains that the hero's origin story, in which Bruce Banner was killed by the gamma bomb and turned into the Hulk for the first time, was "the first demonstration of his immortal nature."
The two brawlers have fought beyond these two encounters, but these two fights establish a few hard facts: the Hulk can be overpowered by the Juggernaut; the Hulk cannot consistently stop the Juggernaut; and most importantly, the Hulk's strength, even at maximum, cannot harm the Juggernaut at his maximum power.
A battle between Superman and Hulk's ultimate form goes to the Breaker of Worlds on sheer power, but given the One-Below-All's planet-destroying plans and Kal-El's history with Krypton, it's likely the Man of Steel would give everything he has to take down a threat that is in many ways his exact opposite.
The Maestro is defeated when the Hulk lures him back into the rebel's base—the Maestro throwing Rick Jones into Wolverine's skeleton in the process— subsequently using Doom's time machine to send the Maestro back to the time and place that the Hulk was created: ground zero during the testing of the atomic Gamma Bomb.
WHY HE CAN'T: The Hulk Has A Limited Range Of Powers. Despite the power-up and new abilities of the Hulk, Darkseid's power is seemingly infinite. Nothing the Immortal Hulk could dish out is something Darkseid wouldn't be able to counter.
Clearly, Thanos is aware he wouldn't be able to lift it. Although it's hard to pinpoint what exactly makes someone worthy of using Mjolnir, as it's ultimately determined by Odin, who placed the enchantment on the hammer, some believe one's worthiness is measured by traits like courage, honor, and selflessness.
Who would win, Deadpool or the Hulk? Deadpool may be able to regenerate but no matter how many times he gets back up or reattaches his head, the Hulk will always smash him back down.
Zeus almost undoubtedly takes this. Hulk, even in his World Breaker form, would have an extremely low probability of winning. First of all, Zeus is a top tier Marvel Skyfather and in many ways similar to Odin who is immensely powerful.
If it's a battle to the first victory Hulk wins. If it's a battle to the most victories, it's a tie. Neither of these characters can die permanently. Doomsday will almost definitely perish in their first fight because this Hulk has been shown to be incredibly powerful, ruthless, durable, and intelligent.
FIXIT - WEAK. Remember that Gray Hulk might be the weakest version of the Hulk of all-time but there was one other time that Hulk went gray after that original appearance. This was when he turned into Mr. Fixit.
