'Deadpool 2' Teases Major X-Men and Avengers Crossover

Deadpool 2 just opened in theaters and the film is full of Easter egg references to Marvel and DC Comics characters. One of those Easter eggs may foreshadow a major crossover between the X-Men and the Avengers.

SPOILERS for Deadpool 2 follow.

In Deadpool 2, Deadpool teams up with Colossus and Negasonic Teenage Warhead to deal with a troubled mutant named Firefist who lived at the Essex House, an orphanage for wayward mutants.

It turns out Firefist had a good reason for wanting out of Essex House. The headmaster was an anti-mutant fanatic who tortured the mutants staying at the facility, trying some form of conversion therapy on them.

Toward the end of the film, everyone involved in Fireifst's story ends up back at the Essex House. This time, they go inside and the headmaster's anti-mutant regalia can be seen in plain view. These include banners and flyers referencing "M-Day."

While M-Day is never explained in the film, some Marvel Comics fans may remember it as a reference to House of M, a major Marvel Comics crossover event featuring both the X-Men and the Avengers that was published in 2005. The event was one of the biggest, most impactful, and most important in X-Men and Marvel Comics history.

House of M was specifically meant to be a crossover between Astonishing X-Men and New Avengers, Marvel's two flagship titles at the time. The story was a follow-up to "Avengers Disassembled," the story that saw the Scarlet Witch go mad and attack her fellow Avengers, killing several of them and leaving the team defunct.

Brian Michael Bendis wrote "Avengers Disassembled" and relaunched the team with New Avengers. He also wrote House of M, with artist Olivier Coipel, and the story begins with the X-Men and Avengers coming together to decide what should be done with the Scarlet Witch.

While the X-Men and the Avengers are debating, Quicksilver fears that they'll decide to kill his sister. He warns Wanda and she casts a spell that alters reality. The world she creates is meant to give everyone what they've always really wanted. The biggest change is that Magneto now rules the United States, which is a society where mutants and humans peacefully coexist, but humans are de facto second class citizens because they cannot compete with mutants and their special abilities.

Wolverine remembers the world the way it was. With the help of a girl named Layla Miller, Wolverine joins with a human resistance group, awakens the memories of several other X-Men and Avengers, and together they take the fight to Magneto, whom they assume is responsible for Wanda's spell. When the truth is revealed, Magneto turns on Quicksilver and beats him nearly to death.

At that point, Scarlet Witch realizes they can never be happy as long as mutants exist. She speaks the fateful magic words "No More Mutants" and returns the world to normal, except that nearly every mutant on Earth has lost their powers. Less than 200 powered mutants remain.

The day that the mutants lost their powers came to be called M-Day. The result was known as the Decimation. This event set the stage for years of storytelling surrounding both the X-Men and the Avengers leading up to the rebirth of the mutant race at the end of the Avengers vs. X-Men event in 2012. Could Deadpool 2 be laying the potential groundwork for the X-Men to join the Marvel Cinematic Universe?

For her part, Scarlet Witch actress Elizabeth Olsen has said that she'd be interested in making a House of M movie.

'I would love to [do a standalone], and I would love it to be House Of M, which is a comic book series of The Vision and Scarlet Witch having a make-believe family," Olsen said. "She [Wanda] believes she has twin children – she alters her own reality to believe that, but really she has a miscarriage and Vision goes along with it. Then they [Vision and her family] have to tell her that she was make-believing the entire time, and she has a very traumatic experience and screams, and kills all the mutants – but that's an X-Men story so we'd have to adjust the ending."

Or maybe you wouldn't if the Disney purchase of 20th Century Fox goes through.

Deadpool 2 is now playing in theaters.

Other upcoming X-Men movies include X-Men: Dark Phoenix on February 14, 2019, Gambit on June 7, 2019, and The New Mutants on August 2, 2019.