The post-credit sequence for the “Captain Marvel” sequel reveals Monica Rambeau (Teyonah Parris), trapped in a different universe and lying on what appears to be a hospital bed beneath the X-Mansion — The X-Mansion from Fox’s adaptation, specifically. The two biggest clues indicating this are the sterile, white aesthetic and the inclusion of Kelsey Grammer as Dr. Hank McCoy, aka Beast. He looks a little different than “X-Men” fans might be accustomed to, what with his being digitally rendered as opposed to having Grammer wear practical makeup, but it’s definitely him. He’s not the first Fox actor to cross over, but he is the first to not be immediately killed or otherwise wasted on a humorless erection joke.
Meanwhile, on Earth-199999, “The Marvels” concludes with Carol Danvers (Brie Larson) and Kamala Khan (Iman Vellani) confident in their ability to rescue Monica. As the MCU’s first confirmed mutant, Kamala’s connection to this narrative arc feels important, but it also complicates things. If she’s a mutant, then there’s a small possibility that some version of the X-Men already exists in the primary continuity and that they’ve actually been around this whole time. Following that thread to its natural conclusion would mean that Professor X and his super school, packed with proactive superheroes, chose to ignore every single major event in the MCU … which would suck. A lot. So let’s pretend that’s not even a possibility.
And while “Deadpool 3” is set to bring both Ryan Reynolds’ Wade Wilson, aka Deadpool, and Hugh Jackman’s Logan, aka Wolverine, into the MCU, how are the rest of the mutants going to make their entrance? Well, that’s where Mister Sinister could come into play.