With every superhero movie comes at least one villain for the main protagonist(s) to face off against, and the Marvel Cinematic Universe has brought in a lot of baddies over the last decade. A few of these villains managed to survive their introductory appearances, but most of the MCU baddies have been killed off after their sole appearance. As it turns out, the character that's killed the most main antagonists in this film franchise isn't one of the heroes, but actually a supporting character: Pepper Potts, Tony Stark's confidant-turned-love interest-turned-fiancee.
As recently noted in a Reddit thread, so far Spider-Man and Wasp are the only two titular MCU heroes who haven't killed anybody yet, but one of the commenters noted that when it comes to the leading villain deaths, Pepper Potts ranks at the top of the list. First, she overloaded Stark Industries' central arc reactor in Iron Man, which electrocuted Obadiah Stane, a.k.a. Iron Mongerm and caused him to fall into the reactor, with the following explosion finishing him off. Then in Iron Man 3, an Extremis-powered Pepper killed Aldrich Killian, a.k.a. The Mandarin (not really), with some Iron Man tech. Pepper wasn't responsible for Ivan Vanko's demise in Iron Man 2, but she aided in having Justin Hammer arrested, so that makes for a nice consolation prize.
Rocket Raccoon could technically tie with Pepper Potts, but his villain kills have been part of a group rather than on his own. He, Star-Lord, Gamora and Drax incinerated Ronan the Accuser in Guardians of the Galaxy, and in Guardians of the Galaxy Vol. 2, he built the bomb that Groot placed next to Ego's brain. When it comes down to it, Pepper has taken down more main antagonists in the MCU on her own than anyone else, and she's not even in the superhero game. Well, she's superhero-adjacent, but that's not the same as going out regularly to fight bad guys in a costume.
After a four year-absence from the MCU, Gwyneth Paltrow reprised Pepper Potts later year for a cameo towards the end of Spider-Man: Homecoming, and she also briefly returned earlier this year in Avengers: Infinity War. With Tony and Pepper finally having patched things up, the two are now engaged, but while the couple were chatting in Central Park at the beginning of Infinity War, Tony was pulled away by Doctor Strange to join the coming battle against Thanos and his forces. We all know how that turned out, but the movie didn't reveal if Pepper was one of the people who faded away after the Thanos snap. That being said, it appears that Pepper may have survived, as back in May, Paltrow stated that when we see Tony and Pepper in Avengers 4, they're now married and have a child. This has yet to be officially confirmed, but if Pepper will be looking after the little one while Tony and his remaining allies try to undo what Thanos did, then don't expect her to eliminate any enemies, let alone the Mad Titan himself!
It looks like Gwyneth Paltrow will be back as Pepper Potts when Avengers 4 comes out on May 3, 2019, but before that, the MCU will continue when Captain Marvel flies into theaters on March 8, 2019.