Originally Posted by
Grunty
Using the reveal of who the Power Broker was in Falcon and the Winter Soldier, i would go with a 3 phase plan using a twist on the Power Broker.
Phase 1. Introduce less important mutant characters as super powered henchmen or little oddities in current or upcomming movies/series set on Earth.
This way the MCU gets a series of characters who have unexplained super powers, but aren't as famous or powerfull that they couldn't just be "broad strokes" assets, ala Taskmaster in Black Widow to the common viewer.
In case of the henchmen however they would all have in common that it was the Power Broker who mediated them and offered their services to the respective villains or evil organizations. Similar to how she hired Batroc.
Make the viewer think that their powers are tied to the "super soldier arms race" that was re-introduced in Falcon and the Winter Soldier and that Power Broker just found another scientist to work on new serums. Being C and D listers would then also make it easier for viewers to not be bothered if they don't survive their appearances.
Characters to use could be the Mutant Force, Alliance of Evil members who weren't Frenzy, some of the shorter lived Acolytes, most of the Dark Riders, some of the Upstarts, some of the MLF, some of the S-men, some of Gene Nation, The Nasty Boys, etc.
But among them, would also be one or two more valuable C-listers who survive and be used again later. Characters who can make an impression but aren't too big.
Phase 1. would then end with a major reveal about the Power Broker. She isn't Sharon Carter. The real one escapes from a prison, where she had been held in since the end of Civil War. The real Power Broker is none other than Raven Darkholm, aka. Mystique and she has been active for a while.
Phase 2. Setting the stage.
Now that the viewer know mutants are a thing in the MCU and that some seem to have been active for a while, the mutants are officialy introduced in the MCU as part of the ongoing "shadow war" on Earth where everyone wants to get their hands on super powered people. This is also when the heros officialy learn of mutant and meet future X-men characters.
For example a hero could encounter FBI agents "Slim" and "Red" in a case about a missing kid who had "weird abilities", only to later learn that they aren't FBI agents as they claim, but that they were just holding up blank pieces of paper "Agent Red" then made everyone belief contained real IDs.
Or a hero could be captured by some pirates in Africa and meeting a friendly black south african in their cell. He tells them he was captured trying to steal something from the pirates back, which they took from a small village, who's "god" he owes a favor.
He then helps the hero escape by making the wall of their cell "dissolve" off screen and the hero slightly disgusted. Then in the post credit scene he is seen walking in the desert worn out but determinded, only for rain to suddently drop on his shoulder. Cheering and looking up the viewers then see a massive raincloud incomming with a mysterious female figure inside.
Finaly Mutants are properly explained in one movie or series which also features some later X-men members, when "lost" SHIELD files are uncovered to defeat a villain who turns out to be a mutant who got his powers boosted by a secret experiment long ago.
This reveals that mutants have always existed in the MCU, but before the "Thanos Snap" there had only been very few. Like 100 total worldwide at most times.
SHIELD started investigating them with "Project Black Womb" which eventualy got shut down by a young SHIELD agent named Charles Xavier in the 70's, when they begann to performing experiments on children. Xavier himself gathered a team (including the allready 100 year old Raven Darkholm and her lover Iren Adler, a young Magneto, his foster brother Cain Marko and the later villain) and hunted down the now rogue leader of the project.
Before convincing everyone to burn the files of the project and "forget about it". Only keeping a copy of all files himself.
However ever since the snap the number of mutants is dramatically increasing per year and they soon will become frequent enough that the media will notice. This sets the stage for the X-men movie proper.
Phase 3. The X-men are assembled and the rest of the franchise will follow.
After several of the important X-men and their villains had been introduced in Phase 2. The X-men are officialy gathered when old machination by the long disappeared Xavier and Magneto spring into action, ultimately revealing mutants to the world and changing the super powered landscape of MCU's earth.
The exact team members would depend on the build up and how the story would need them. Though i would go with a good mixture of 05 and ANAD.