MCU: 10 Best New Villains Who Could Join Phase 4

9. Onslaught

One of the best ideas for bringing the X-Men into the MCU is to further explore the possibility of alternate dimensions already posed in both Ant-Man and Doctor Strange and have them cross over from an entirely different version of Earth (perhaps one that has already been destroyed). And the reason for them coming to the Earth of the MCU could be the arrival of a threat they feel partly responsible for who they could have the knowledge to defeat combined with other Marvel heroes.

That threat could be Onslaught, the combined entity born when Magneto and Professor X unwittingly merged and who possesses all the powers of both mutants along with enhanced physical strength and size. This approach would mean we'd have a ready-made world-ending threat alongside the arrival of his enemies without the need for an origin for either.

And he's such a powerful villain that he'd definitely live up to the billing.