10 Unused X-Men Villains MCU Phase 4 Could Introduce
1. Mr. Sinister
Who? Nathaniel Essex is not technically a mutant. He's genetically altered himself to have abilities. He became a telepath, figured out how to live longer, made himself a shape-shifter, and has a way to teleport. He's possibly been alive since the 1800's. He's been a shadowy figure though-out the comics, cartoons, and was even hinted at in the Fox franchise.
Mr. Sinister is exactly who the MCU should unleash in their universe. He's had a hand in messing with the Summer-Grey family, worked with Apocalypse, and had a hand in the weapon-x program.
How he fits in the MCU: Disney-Marvel have their two choices: mutants are a new thing or they've been around and just haven't mentioned them yet. Sinister fits in both. He can be shown in his origin in the 1800's, working with Charles Darwin, discovering the evolution of mutants. He can be inserted in the continuity of previous MCU titles, similar to how Hydra was worked in later.
Using him can set up origins for other X-Men characters. Alternatively, the MCU decides that mutants are a new thing, something causing changes in random humans after all the energy involved in "the blip". Essex is a scientist/businessman with a special interest in these powerful beings and looking for a way to study/harness these powers for himself.
Yet again, Deadpool 2 had a Mr. Sinister reference with The Essex House for Mutant Rehabilitation.
Will the Merc with a Mouth really be MCU's answer for all things X-Men?