The X-Men have officially arrived in the Marvel Cinematic Universe, with a new teaser for Avengers: Doomsday showcasing Patrick Stewart as Professor Charles Xavier, Ian McKellen as Magneto, and James Marsden as Cyclops. The teaser, the third in a series of four, debuted after a week of online leaks and is currently playing in theaters ahead of Avatar: Fire and Ash.

The highlight of the X-Men teaser is undoubtedly Cyclops, portrayed by James Marsden, unleashing a massive optic blast. Cyclops is clad in a comic-accurate blue-and-yellow costume reminiscent of the 1990s X-Men cartoon series. This marks a departure from the black leather outfits of the original Fox films, signaling a new, improved Cyclops that finally delivers on Marsden's potential.

Adding to the stakes, the teaser also provides a glimpse of the Sentinels, the giant mutant-killing robots from the X-Men comics. These Sentinels appear to be on a massive scale, staying true to their comic book depictions.

The teaser also reveals Xavier's School for Gifted Youngsters in shambles, with Xavier and Magneto playing chess, a nod to their relationship in previous X-Men films. Magneto delivers a haunting line, "Death comes for us all. It's all I know for sure," adding to the sense of impending doom.

Alongside Stewart, McKellen and Marsden, other X-Men characters confirmed for Avengers: Doomsday include Channing Tatum as Gambit, Alan Cumming as Nightcrawler, Rebecca Romijn as Mystique, and Kelsey Grammer as Beast.

Avengers: Doomsday, directed by Anthony and Joe Russo, involves characters from across the multiverse and a story involving Robert Downey Jr.'s Victor Von Doom/Doctor Doom. The film is set to be released in theaters on December 18.

The previous teasers have highlighted the return of Chris Evans as Steve Rogers and Chris Hemsworth as Thor. The fourth and final trailer is rumored to feature Shuri and M'Baku of Wakanda, Namor, The Thing and possibly Doctor Doom.