The first time Deadpool kills the Thanos is in Gerry Duggan, Brian Posehn, Scott Koblish, and Val Staples' Deadpool #45, "Deadpool Roasts The Marvel Universe." In the comic, Deadpool is hired by Thanos to steal the Cosmic Cube - the last infinity stone he needs to put into the infinity gauntlet.
In the present, Thanos brutally beats up Deadpool while Death is watching. Thanos says that he will take back the gift of immortality he once gave to Wade.
This is actually a rumor. Deadpool didn't kill the entire Marvel Universe any more than Superman turned evil, or Batman killed Joker. The storyline where Deadpool infamously killed the Marvel Universe occurred outside of main comics canon.
Deadpool might have his fair share of comedic moments in the Marvel universe, but the mercenary's powers allow him to be one of the strongest Marvel characters, proficient enough to defeat and kill major Marvel heroes ranging from Captain America to The Fantastic Four.
A mercenary for hire, he played an important role in the series Deadpool; T-Ray served to remind Wade Wilson, also known as Deadpool, what a failure he was. He is Deadpool's archenemy for many issues and almost everything that happened to Deadpool was a part of an elaborate plan orchestrated by him.
He then takes on the Hulk, who easily dismembered Deadpool and proceeded to leave, declaring that he wanted to be left alone. While sleeping, however, the Hulk reverted back to Bruce Banner and Deadpool tracked him down in a cave and killed him.
Deadpool crushing Thor with his own hammer remains one of his most brutal and genius kills, as using the powers of the Pym Particles to expand Mjolnir in size makes the mighty weapon even too massive for the God of Thunder to control.
He is somewhat the same in the comics, so if Deadpool ever faced Thor, the god of thunder would have the winning edge. It's true that Deadpool managed to terminate Thor using Pym Particles in a non-canon comic by enlarging Mjolnir. But MCU Thor never needed Mjolnir in the first place.
But the one being Thanos hates more than anyone is the Merc With A Mouth himself, Deadpool – a rivalry that MCU fans are likely going to miss. While many fans may not expect this rivalry, Thanos and Deadpool have been at odds for quite some time.
Wolverine and Deadpool have fought many times, each getting some wins. However, Deadpool probably has a lead in wins and losses between the two. Wolverine definitely can beat Deadpool and is stronger than him, but Deadpool's speed and healing factor have allowed him to get the drop on Wolverine and do a lot of damage.
Spider-Man wins against any street-level hero in the Marvel Universe, including Deadpool. Put aside Spidey's vastly superior strength, speed, and agility.
In the end, Deadpool wasn't worthy. While he seemingly had control of Mjolnir and the strength of Thor, it was all a mirage put on by Loki to distract Thor.
As you all know, Wolverine kills Deadpool at the end of X-Men Origins:Wolverine, but somehow Deadpool returns around 30 or so years in the movie timeline later for 2 more solo movies and another one upcoming.
In a fight, Loki would win 10/10. Who will win a fight between Lobo and Deadpool? Lobo, hands down. Sure, they're both insane and have crazy levels of being able to regenerate, but the Main Man has a couple of distinct advantages over the Merc with the Mouth.
Steve Rogers is one of the few mortals able to not only lift Mjolnir, but wield its full power, making him someone who legitimately could defeat Thor. Assuming the reason for their battle is due to Thor being deceived, possessed, or otherwise out of his mind, Cap would be able to use Mjolnir against him.
Deadpool's healing factor makes him a worthy opponent for Superman. Sure, Superman could rip him apart, but Deadpool could keep putting himself back together until Superman becomes just as annoyed with his powers as everyone else is with his mouth.
Deadpool then uses the puppets created for him by Puppet Master to kill several cosmic heroes and villains, including the Silver Surfer, Thanos, and even Galactus.
Doctor Doom was among the many heroes and villains killed by Deadpool. He's only ever shown hanging from electrical pole wires, possibly being shocked to death from them by Dreadpool.
Deadpool appears behind Deadpool wearing Beast's skin as a cloak and holding a sword. Wolverine attacks Deadpool, but Deadpool reveals that his sword is made of carbonadium, which can nullify Wolverine's healing factor, and impales him with it.
Deadpool is easily one of the most powerful characters Marvel has. The fast-talking gunman seems almost fearless on the battlefield, but in reality, there's a lot that scares the Merc with the Mouth. There are two things though, that scare him above all: cows and clowns are a Deadpool weakness.
As such, Zeus decides to grant the Hulk's request to beat him to death in hand-to-hand combat. The Hulk's first blow sends Zeus crashing into a nearby building. Zeus then returns this with an even more powerful blow. The ruler of the Olympians than overpowers the Hulk, and ultimately knocks him off Mount Olympus.
