Over the last 13 years, the MCU has introduced dozens of villains and has killed off about half of them, most after only one movie appearance. However, the other half that is still alive, and somewhat well, have been in MCU limbo since their last appearance anywhere from two to 13 years ago.
Many villains were captured and have presumably been imprisoned for many years. However, with the fall of S.H.I.E.L.D. and the Snap, many villains slipped through the cracks. With so many powerful and resourceful villains still roaming around the MCU, it would be a shame for Marvel to not revisit some of these fan favorites.
12 Hulk's Evil Counterpart: Abomination (& Thaddeus Ross to a Lesser Extent)
Abomination was introduced in the second-ever MCU film, The Incredible Hulk, and hasn't been seen since. Though Abomination has been loosely referenced by Bruce Banner and even gets mentioned in the no-longer-considered-canon Agents of S.H.I.E.L.D. Marvel Studios has recently confirmed that Tim Roth's Abomination will be making his return in the upcoming Disney+ show, She-Hulk. Whether or not Abomination will be the villain of the series or if he is able to revert to his human form remains to be seen, though fans are excited to see him return.
Thaddeus Ross has maintained a steady role in the MCU since his introduction in 2008. He was also heavily teased in The Falcon and The Winter Soldier (TFATWS) but never arrived. There is a good chance Ross will cameo in She-Hulk, perhaps finally becoming the fan-favorite Red Hulk. However, before then, fans could see a Ross cameo in Black Widow.
11 The Poor Man's Tony Stark: Justin Hammer
While Justin Hammer was more of a joke character back in Iron Man 2, he still posed a serious threat because of his wealth and resources. Once he realized he had backed the wrong horse in Ivan Vanko, the villain Whiplash, he attempted to right his wrong by helping Pepper and Natalie (actually Natasha) crack the encryption on his suits.
However, he was too late and was carried away in handcuffs, promising to make a problem for Pepper and said he would be seeing her real soon. Hammer has not been seen in the MCU since that moment. With Tony gone from the MCU, Hammer could potentially reappear as a ground-level threat in Armor Wars or Ironheart. With Sam Rockwell in the role, it would be a shame if Marvel didn't find a way to bring back this quirky and charismatic villain.
10 Cap's Nazi Equivalent: The Red Skull
When fans first saw Red Skull get absorbed into the beam created by the Tesseract, they all assumed he had perished. However, once the powers of the Tesseract were truly understood, fans realized he may still be alive. Fast-forward to over 70 years later and Red Skull had been on Vormir the whole time protecting the sibling of the Tesseract, the Soul Stone.
A huge hope of fans is a show where each episode reveals how Steve returned the Stones to their respective places in time; fans are most curious about the Soul Stone for his interaction with the Red Skull. With the multiverse set to be coming in the Dr. Strange sequel, fans may meet another version of Red Skull where maybe he was Erskine's hero instead of Steve.
9 Don't Count Out the A.I. Known As Ultron
While it's assumed that Vision destroyed Ultron at the end of Avengers: Age of Ultron, it isn't actually shown on screen, leaving things a bit ambiguous. It's also worth noting that the Ultron bots that were a part of the A.I.'s hive mind were shown to have glowing eyes, when the bots were destroyed, their eyes stopped glowing. In Spider-Man: Homecoming, Peter stumbles across an old Ultron head in a Damage Control truck and the eyes are glowing red.
Whether or not this means anything, has yet to be confirmed by Marvel, leaving the potential for an Ultron return wide open. Many fans even expected Ultron to make a cameo in WandaVision as he was such a traumatic part of Wanda's life, and James Spader was mistakenly shown as a cast member on Google. Given Ultron's propensity to return from the dead in the comics, fans should expect to see an Ultron return at some point.
8 The Brilliant Darren Cross, aka Yellow Jacket
While many fans believe that Cross died when his suit malfunctioned in the first movie, fans have also been shown that people can survive in the Quantum Realm for decades. Peyton Reed has also coyly suggested that Cross could be down in the Quantum Realm somewhere, floating about waiting to be revisited.
Cross may very well make a return in Ant-Man and the Wasp: Quantumania. Considering the movie is expected to dive deep into the Quantum Realm, and the director himself has teased that Cross could still alive, Cross is poised for a cameo. Paired with the recent presumed leak from The Wasp herself, using a bee emoji when posting about reading the script, Cross may be making an unexpected comeback.
7 The Cool & Calculated Baron Zemo
Zemo recently made a return to the MCU as a major part of the sensational TFATWS show. Though by the end, he was back in prison, this time at The Raft, which is about as supermax as a prison can get. The events of TFATWS appear to be setting up a Thunderbolts team, strategically placing Zemo and Thaddeus "Thunderbolt" Ross in the same building.
Paired with the introduction of U.S. Agent, another member of teams such as the Thunderbolts and the Dark Avengers, it seems likely that Zemo will make another appearance in the recently announced Captain America 4 movie. With U.S. Agent, Zemo, and a slew of other anti-heroes lying around, this movie seems like the perfect time for the Thunderbolts to come to fruition.
6 Dr. Strange's Dormammu of The Dark Dimension (& Maybe Kaecilius)
While Dormammu did make a promise to never return to Earth, who's to say he's an interdimensional being of his word? There is also a chance that he learned of the destruction of the Infinity Stones, including the Time Stone, which was Dr. Strange's only real defense against Dormammu when the sanctum barriers were compromised.
If Dormammu or Kaecilius did return, Doctor Strange into the Multiverse of Madness would certainly be a logical place for them to do it. While it is highly unlikely for Dormammu to return as the primary antagonist, he could have a cameo or pop up down the line in a third Dr. Strange film.
5 Old-School Hero Turned-New School Villain: Vulture
Micheal Keaton does a great job of being a likable villain, and with the foreshadowing of the end-credits scene in Spider-Man: Homecoming, fans might expect to see Vulture return in the third Spider-Man movie. Keaton is already confirmed as being in the upcoming Sony-verse film, Morbius, though whether or not he is reprising his role of Adrian Toomes has yet to be confirmed.
Though if it turns out that he is playing the same character in Morbius, fans should expect Keaton's Vulture to play a more significant role in the MCU and the Spider-verse going forward. Perhaps the heavily rumored Sinister Six has been given the green light.
4 The Mysterious Quantum Entangled Girl: Ghost (& Maybe Sonny Birch)
Ghost (Eva) appeared to have figured out a solution to her ailment by the end of Ant-Man and The Wasp, allowing her to leave behind her life of villainy. However, it's unknown if she was dusted during the Snap or if she was left behind while team Ant-Man, who had been the source of her medicine, dusted into oblivion.
Fans might expect her to return to her life of crime, especially if Bill Foster was dusted as well. Assuming there isn't already too much going on in Ant-Man and The Wasp: Quantumania, fans might expect Eva to return either as a minor villain or a still trusted ally. Sonny Birch was presumably imprisoned at the end of the second film, but fans never learned who his mysterious benefactor was, so perhaps the Little Weasel will make another appearance as well.
3 The Kree Mercenary: Yon-Rogg (& The Supreme Intelligence Back On Hala)
At the end of Captain Marvel, Carol sent Yon-Rogg back to Hala with a very specific message for the Supreme Intelligence, so fans might be expecting these two to return in The Marvels. However, with new heroes being introduced such as Ms. Marvel and presumably Monica Rambeau's Photon, there is a pretty significant chance that this movie won't be a period piece like the first one.
This would indicate that it will have taken Carol since 1995 to finally make it back to Hala to seek her revenge against the Supreme Intelligence and presumably settle some final score with a disgruntled Yon-Rogg. Or, it would indicate that Yon-Rogg, The Supreme Intelligence, and Hala may fall by the wayside to make room for the new heroes.
2 The Master of Illusion: Mysterio (May Have Faked His Death)
While Mysterio is believed to have died at the end of Spider-Man: Far From Home, many fans think he may have faked his death and was the one who outed Peter as Spider-Man. Mysterio was depicted as a villain that was always several steps ahead, one that relied more on brains than brawn.
It would come as no surprise to fans if Mysterio pops up in the next Spider-Man film, perhaps helping to form the heavily teased Sinister Six. Mysterio may even appear in the next Dr. Strange film as a call back to his character claiming to be from another universe in Spider-Man: Far From Home.
1 The Ancient Witch from Salem: Agatha Harkness (& Wanda, Until More Is Explained in Dr. Strange 2)
Despite being a massively powerful and magical threat, Wanda felt content leaving Agatha living in Westview under the influence of a spell keeping her in a neighborly façade. The small exchange before Wanda hexes her forebodes a big return for Ms. Harkness at some point down the line.
With all of the hype around the Dr. Strange sequel, she could even pop up in that movie. Perhaps WandaVision will be renewed for a second season and fans will see Wanda developing her powers under the tutelage of Agatha. Perhaps Agatha may break free from Wanda's spell and become the next major villain for a completely different hero. On the other hand, whether or not Wanda is a true villain remains to be seen, but she will definitely be appearing in the Dr. Strange sequel, so hopefully, fans will get an answer.