WARNING: The following contains spoilers for What If...? Season 1, Episode 3, "What If... the World Lost Its Mightiest Heroes?," now streaming on Disney+
Due in part to his almost comical name, Ant-Man has been considered something of a joke character in the Marvel Cinematic Universe. But thanks to the Pym Particles that power the Ant-Man suit (as well as other similar designs), Ant-Man is theoretically one of the most fearsome killers in the Marvel Universe. All it takes is the right person with the right motivation to make the concept into a genuinely horrifying one.
For example, take Hank Pym in What If..?, who proved that with a shrinking suit in his hands and vengeance in his heart, he could become the most prolific killer in the Marvel Universe and single-handily kill off most of the Avengers before they even formed the team.
In the MCU, Hank Pym was reinvented as a genius SHIELD inventor and a secret superhero. Serving as Ant-Man alongside his wife Jan as the Wasp, the duo save countless lives over the years -- with Wasp eventually disappearing on a mission and presumed dead upon shrinking herself into the quantum realm. This led Pym to eventually leave SHIELD and develop a strained relationship with their daughter Hope, who never fully knew the sacrifice her mother had made. Eventually, though, Pym was forced to tell her the truth during the events of Ant-Man, resulting in Hope taking a more pro-active role in the world and becoming the Wasp alongside the new Ant-Man, Scott Lang.
However, a minor innocuous change to the timeline could have radical effects, such as in What If...?. In one reality, Nick Fury ended up telling Hope about her mother's role in SHIELD years earlier, resulting in her becoming inspired to follow in her mother's footsteps and become an agent herself. However, Hope wouldn't survive her tenure with SHIELD and was killed years earlier than in most realities. This drove Pym further off the edge, setting him up to fully embrace a plan of vengeance against Fury. This took the form of derailing his plans to assemble a team of heroes that would go on to become the Avengers Initiative -- and to assist him, Pym stole the Yellowjacket suit to enact his revenge.
Coupled with his own brilliance and the Pym Particles that let him control his size, Pym proved able to effectively wipe out the Avengers before they even formed. His intervention at key moments resulted in Iron Man, Thor and Hulk -- three of the most powerful Avengers -- all wiped out in seconds. Hulk, in particular, had a brutal death, with Pym's intervention resulting in the Jade Giant's body blowing up like a balloon and popping instead of transforming him into one of Earth's most powerful protectors. With the Yellowjacket suit, Pym could sneak up on the eagle-eyed Hawkeye and kill him with relative ease. He even went head-to-head with the lethal Black Widow and more or less defeated her, his decreased size allowing him to get the better of her.
With just a little bit of effort and a lot of motivation, Hank Pym proved just how lethal an Ant-Man could be, especially with him under the helmet. The only reason he even stopped was because of Nick Fury making a figurative deal with the devil by allying himself with Loki. Someone with the Pym Particles could quickly prove dangerous enough to bring down gods and Hulks all on their own, with no one the wiser. It was only through Black Widow's final transmission to Fury that the latter uncovered Pym's involvement, and even then, there was little he could do except goad Pym into exposing himself so Loki could help bring him down.
It's even a reminder of how dangerous someone as much of a goofball as Scott Lang could become if he went through a similar loss with his daughter Cassie. Of all the MCU heroes, Ant-Man has always had a lot of deadly potentials -- and What If...? showcases just what someone can do with it in the most horrifying way possible.
To see Earth's Mightiest Heroes fail to form in the MCU thanks to Yellowjacket, the third episode of What If...? is streaming now on Disney+.