A while ago, we learned that Doctor Strange in the Multiverse of Madness is currently undergoing reshoots to either reshoot some of the scenes or film additional scenes that they weren't able to do during principal photography due to logistical reasons related to the pandemic. Now, it looks like there are more reasons behind the reshoots.
According to The Hollywood Reporter's recent Heat Vision newsletter, as a result of Spider-Man: No Way Home and Loki (which both deal with the multiverse), Marvel decided to have "more fun with the multiverse" in Doctor Strange in the Multiverse of Madness which is why they were undergoing reshoots to include more cameos and character introductions in the film.
Given the endless possibilities of the multiverse, there's a lot of characters who can potentially make an appearance in the film. For a while, there have been rumors that Patrick Stewart will be reprising his role as Charles Xavier in the film. There are also rumors and whispers that characters such as Mister Fantastic and Magneto will also be making an appearance. Of course, none of them has been confirmed yet.
The question now is who are the characters that we might be seen making a cameo appearance in the film? There's obviously a lot to choose from. It could be a variant of an already existing MCU character or a character from What If...? appearing in live-action form. There's also a possibility that we might see a Marvel Comics character who hasn't appeared in the MCU make an appearance such as the X-Men characters or the Fantastic Four. But whoever they are, as the title suggested, it's going to be madness.
A teaser trailer for the film was recently shown as the post-credits scene of Spider-Man: No Way Home. However, it hasn't made its rounds online yet although you can see several camcorder versions around the web as it leaked days before the film's release. Based on the teaser trailer, it does look like the film will be bonkers and there's more to come besides what they've shown.
Doctor Strange in the Multiverse of Madness is set to be released in theaters on May 6, 2022.