Here's who that mysterious figure was in the credits scene of "The Fantastic Four: First Steps" and how it sets up Doomsday.

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

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.