'Deadpool 2' Drops Major Mr. Sinister Easter Egg

One of the X-Men's greatest villains from the comic books has yet to make an appearance on the big screen, but that doesn't mean it's not in the works.

After first being teased in the post-credits scene for X-Men: Apocalypse, the classic baddie Mister Sinister was referenced yet again in Deadpool 2.

Warning: Spoilers for Deadpool 2 below.

It's to be expected that any film featuring the Merc' With the Mouth would be packed with references and easter eggs not limited to what 20th Century Fox has rights to, as evidenced by referenced to both Avengers: Infinity War and Batman v Superman: Dawn of Justice.

But it also remained very faithful to the X-Men mythos, adding Juggernaut as a (not-so) surprising villain who even referred to Professor X as his brother. But it's the villain Mister Sinister who looms in the background, possibly being set up for the X-Force movie.

In the film, Julian Dennison's character Russell Collins grows up to become a criminal who eventually kills Cable's family, prompting the militant mutant to time travel to the past to prevent this from happening.

In Deadpool's present day, Russell lashes out at his tormentors of the Essex House for Mutant Rehabilitation, and later he and Juggernaut return to the building to kill the headmaster.

Essex is an obvious reference to Mister Sinister, who also goes by the name Nathaniel Essex as one of his numerous alter egos. This is also the second time Essex has been name dropped directly, as the Essex Corporation appeared on a briefcase in the post-credits scene for X-Men: Apocalypse, when an unnamed official was seen procuring Wolverine's blood from the Weapon X facility.

It was assumed this would pan out to set up Logan, though the character had nothing to do with that bleak exploration of the X-Men's future. Now, some theories posit that Jessica Chastain will be playing a female version of the villain in X-Men: Dark Phoenix, though the character Miss Sinister has also played a major role in recent X-Men comic books.

There's no telling yet just how this will pan out in the future X-Men cinematic universe — it could even serve as a plot thread that will play out in X-Force.

It is only a quick reference in Deadpool 2, but we can't help but wonder if Fox has some long-term plans for the classic X-Men villain.

Deadpool 2 is in theaters now.

Did you notice any other Easter Eggs that we might have missed? Be sure to let us know in the comments!