A new Avengers: Doomsday theory explores how the Fantastic Four might travel to Earth-616. It suggests Reed Richards uses Galactus’ ancient ship tech, combined with his own inventions, to build multiversal transport and rescue Franklin Richards from Doctor Doom’s grasp.

Marvel Studios head Kevin Feige recently teased a meeting between the Avengers, X-Men, and Fantastic Four at the Baxter Building in Avengers: Doomsday. Following the release of The Fantastic Four: First Steps,

The "Doomsday" plot leak also seems to confirm the big fight at the X-Men mansion in the universe where Monica Rambeau ended up at the end of "The Marvels." That universe's anchor being is a Professor X (Patrick Stewart) variant that Doom wants to kill. Interestingly, Earth-616 and Earth-10005 -- where Monica is -- are on a collision course.