Note: Be aware there are spoilers for “The Fantastic Four: First Steps” in the article below.

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,

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,