Stephen Strange’s brisk walk across New York is abruptly and severely halted in the last scene of Doctor Strange in the Multiverse of Madness when a third eye opens on his forehead. Strange later decides to travel with Clea (Charlize Theron) to rectify an incursion he reportedly caused, and his third eye opens again shortly before passing through a portal with her in the film’s mid-credits scene. Stephen’s third eye appears to be identical to the one on the Sinister Strange variation he confronts early in the film on both occasions. Unfortunately, none of the movie’s scenes clarify where the third eye came from or what it’s for, though it’s indicated that having it isn’t healthy for Stephen. Indeed, a dialogue with Wong near the end of Multiverse of Madness suggests that the third eye may be the result of Stephen defeating Wanda with the Darkhold.
Doctor Strange does occasionally featured in the comics with the third eye on his forehead. The Eye of Agamotto, the mystical relic that Strange wears around his neck in the MCU, is usually the source of that third eye. The comic book version of the talisman allows the wearer to relive previous events and see certain facts about a person’s soul, among other things. When the talisman is utilized, it frequently causes a third eye to appear on the wielder’s forehead. However, in the comics, the Eye of Agamotto can only be utilized by good magic users, which Sinister Strange is most definitely not in Multiverse of Madness. As a result, it seems reasonable to conclude that the third eye Doctor Strange presently wears in the MCU will be different from the one he wears in the comics. Strange will have to wait and watch how those disparities express themselves, as well as what problems they may generate.