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.

First Steps kicks off MCU Phase 6 by introducing Galactus, the cosmic World-Devourer. But Galactus isn’t merely a villain with an insatiable hunger; his consumption of worlds is tied to the Marvel Universe’s multiversal cycle of destruction and rebirth,

First Step presented a fully-formed universe and introduced a swathe of characters into the Marvel Cinematic Universe.