10 Unused X-Men Villains MCU Phase 4 Could Introduce
8. The Brood
Who? Creepy, parasitic, giant alien insects! If the MCU chooses to go this route, we may have a 2nd horror-mutant movie to look forward to after The New Mutants drops.
Whoever designs the Brood for live-action will most likely take liberties with their specific design, but they basically have a natural armor from their exoskeletons and mouths filled with big fangs. Things turn even more scary when you learn they reproduce via eggs inside of hosts.
How they fit into the MCU: The MCU has already made the giant leap into space, so discovering new alien races is par for the course. There's obvious similarities to Aliens, so Marvel could definitely go the route of sending a "space force" of new Marvel mutants up to counter the threat.
I think a better route is to take inspiration from Independence Day or Invasion of the Body Snatchers with attacks all over the globe. This gives all the mutants no one knew about a chance to rise up and defend their respective territories and establish X-Men as an international team where the Avengers seem so much more America-based.