The X-Men franchise has had many live-action movie adaptions over the past several decades. From the original X-Men trilogy with Hugh Jackman and Patrick Stewart to the newer series of films starring James McAvoy and Michael Fassbender, the movies have covered many of the most important stories from the Marvel comics.
Somehow, however, many of the team's greatest foes have yet to appear in a blockbuster movie. While the biggest X-Men villains such as Magneto, Apocalypse, and Dark Phoenix have all appeared in the X-Men feature films, there are still plenty of great antagonists that have yet to make it onto the big screen.
10 Shadow King
One of Professor Xavier's most formidable telepathic enemies goes by the name Shadow King. Essentially a monstrous entity that exists within the Astral Plane, the Shadow King is constantly looking for a means of escape through some sort of host body.
Although the powerful, menacing villain has escaped his domain and entered the real world on a handful of occasions, he is always stopped and sent back by Professor Xavier and his team of X-Men. It would be very exciting to see this happen in a live-action movie.
9 The Brood
Following the release of X-Men: Dark Phoenix, it is now clear that the X-Men movies are fully capable of showcasing the teams otherworldly, outer space adventures. One of the X-Men's most dangerous enemies from outer space is none other than the Brood.
A race of insectoid-like aliens, the Brood have tried to take over other planets on multiple occasions only to be thwarted by Xavier and his X-Men. They would make for a group of scary, intimidating foes for everyone's favorite mutant heroes to face off with.
8 Cassandra Nova
X-Men villain Cassandra Nova is what is known as a mummudrai. Mummudrai are parasitic life forms that are born without bodies on the astral plane. In her infancy, Cassandra was psychically connected to future X-Men leader Charles Xavier.
The connection between these two telepaths would not go away when these two characters grew up. Despite being born without a body, Cassandra found a way to take on a physical form and then proceed to become one of the X-Men's greatest enemies of all time.
7 Sauron
The Savage Land is an environment that the Marvel movies have yet to visit. This is quite unfortunate, given how incredibly intriguing, beautiful, and adventure-filled the Savage Land is.
Sauron is what is known as a mutate -- the unnatural cousins to mutants. Often in the comics, mutates are treated as bigger freaks than even mutants are. In a movie, this could be played off as a sympathetic story. Bad guys in many of the Marvel movies are given an interesting backstory and sympathetic stories, so this would make Sauron quite an impressive villain for the team to fight.
6 Onslaught
The psychic combination of Magneto and Charles Xavier, Onslaught is one of the most powerful enemies that the Marvel Universe has ever seen. Somehow, his telepathic abilities are so strong that this villain was able to use his mental powers to construct himself an indestructible physical body.
In his heyday, Onslaught took and defeated not just the X-Men, but also the Avengers, Fantastic Four, and every other hero in the Marvel Universe. It took the seemingly infinitely powerful Franklin Richards to dispatch the villain once and for all.
5 Mojo
Hailing from an alternate reality known as the Mojoverse, Mojo is by far one of the most revolting enemies that the X-Men have ever gone toe-to-toe with. A cartoonish caricature of a television producer, Mojo is certainly the oddest villain to appear on this list.
In the Mojoverse, all beings are addicted to Mojo's gladiator-like television programs. Often times, the character captures X-Men characters and forces them to fight for his large audience. Sure sounds like a very fun premise for a movie.
4 Arcade
Arcade loves to pit his enemies against a series of puzzles and tests inside his own self-made murderous amusement park. A goofy villain, Arcade would fit perfectly within the tone of the lighter MCU films.
Think Saw but more circus-themed and rated PG13. That is what Arcade would be like in a live-action movie and, honestly, it sounds like an amazing breath of fresh air for the Marvel movies that have been criticized several times in the past for following the same formula for all of its movies.
3 Master Mold
The sentinels are one of the most iconic enemies in all of Marvel comics. The look of these robot mutant killers is utterly unforgettable. While sentinels have appeared in the movies, their leader, the Master Mold of the sentinels, has yet to appear.
While sentinels have appeared in the movies, they have yet to appear as an army of antagonists that the X-Men are forced to face for the majority of a feature film. Such a film would be quite exciting. Especially if, at the end of the movie, the X-Men were forced to face off with the incredibly massive Master Mold.
2 Omega Red
Wolverine has faced off with several other killer mutants over the course of his murderous career as a superhero. Omega Red was by far one of the worst enemies that Wolverine ever had to deal with.
A serial killer born in Soviet Russia, Omega Red was experimented on and given retractable carbonadium tentacles in each of his arms. These nigh-indestructible tentacles make him quite the match for Wolverine. They would also make for quite the impressive visuals in a live-action X-Men film.
1 Mister Sinister
Although sometimes portrayed as the right-hand man to the villain Apocalypse, Mister Sinister always has his own plan in motion for attaining ultimate power. Often times in various comic book stories, Sinister is seen manipulating the power and influence of Apocalypse to his advantage.
Bryan Cranston once said that if he were to play a supervillain, he would choose Mister Sinister. Whether that comes to fruition or not, Mister Sinister is without a doubt the biggest X-Men baddie yet to make it into a movie. It will be interesting to see how the actor cast in the role will portray the storied comic book evil genius.