Now that most of the epic comic book fights ever published have been adapted to the big screen, fans and creators alike are on the lookout for the more unheralded matchups from comic continuity - those that might show up in the next few phases of superhero cinematics. Followers of the genre have traditionally debated who would win a superhero fight between their favorite characters, but there are unexpected results out there in the history of both DC and Marvel Comics that make prognosticating difficult.
Generally speaking, it’s a good rule of thumb never to count out a character starring in their comic book - and there are countless upset victories against some of the most powerful villains to prove it. Squirrel Girl has taken down her fair share of mighty opponents, and there are several instances in which one scrappy street fighter overpowers a notoriously strong team. Depending on who is writing the comic, any character can theoretically beat any other character on any given day - it’s all just a matter of crafting the right circumstances.
Spider-Man has the proportional strength of a spider, but even that pales in comparison to the might of an official Herald of Galactus - after all, such beings are imbued with the Power Cosmic! One such individual is Firelord, and he’s gone toe-to-toe with people as powerful as Thor in the past. But in Amazing Spider-Man #270, Peter Parker prevails.
The fight ensues when Firelord comes to Earth looking for trouble and none of the Avengers are available to give it to him. After a few other gambits fail, Spidey - angrier than ever following his run-in with an alien symbiote and still sporting the black costume it inspired - starts throwing hands with abandon. He ends up trouncing Firelord so much that the late-arriving Avengers have to step in to get him to stop - but the astonishment and respect on the faces of Earth’s Mightiest Heroes are apparent.
Daredevil is used to defying the odds - but at the end of the day, he's still mostly an ordinary human with no superior strength or speed. That's what makes it such a shock that he's able to battle an entire Avengers roster to a standstill - especially when that roster contains Hercules, an actual Greek god.
In Daredevil #155, Matt Murdock shows up at Avengers Mansion looking for revenge against Black Widow - and he doesn't care who gets in the way. He stomps all over Captain America, the Beast, and Hercules - leaving each of them in a state of unconsciousness. Fortunately for Black Widow, Daredevil regains his self-control before he moves on to her.
Ka-Zar is essentially Marvel Comics' answer to Tarzan - a non-powered human who grew up in the prehistoric jungles of the Savage Land. When he discovers in Ka-Zar #11 that Thanos is causing havoc in his homeland, he takes him on - and somehow, he walks away victorious.
There are some extenuating circumstances in this matchup. Much of Thanos's energy is being fed into a terraforming machine at the time, so he's not at his best. But that still doesn't explain why an ordinary human can take on one of the strongest beings in the universe. Ka-Zar enjoys a lengthy battle with Thanos that culminates in him booting the Mad Titan into a volcano - though later, this particular Thanos is retconned as a defective clone, robbing Ka-Zar of his upset.
Crossovers between DC and Marvel Comics aren't anywhere near as frequent as they used to be, and that's perhaps with good reason. Such crossovers often depict highly unlikely inter-company matchups - and some even more unlikely results to those bouts.
There may be no more explicit example of this than the time Venom nearly slays Superman in DC/Marvel: All Access #1. Despite being just a stronger version of Spider-Man - and despite Superman being, well, Superman - Venom smacks the Kryptonian around the city for a while before attempting to choke him with his gooey appendages. It's only the timely intervention of Spider-Man that saves Superman from an incredibly ignoble end.