First Steps" has a thrilling ending that teases Dr. Doom and where the MCU goes from here in "Avengers: Doomsday."

But that all changes in the movie's post-credits scene, when the vibe shifts and suddenly there's a metal-masked stranger hanging out in the living room of the Baxter Building. If you've seen The Fantastic Four: First Steps and need some Reed Richards–level tutoring to figure out just what the heck is going on,

The following article contains spoilers for the end of The Fantastic Four: First Steps. If you have not yet seen the movie, proceed at your own risk! The post-credits scene in Thunderbolts* provides fans with some big revelations about the future of the Marvel Cinematic Universe.