Stranger Things' Sadie Sink is officially joining the MCU, making her debut as an unknown character in Tom Holland's Spider-Man 4. This Sadie Sink casting theory completely flips the idea of what Spider-Man 4 could be on its head.
Sink could be playing a variety of characters, with the leading theory being Jean Grey, joining the MCU's roster of X-Men. However, a fan theory has gained momentum, leaning into the previously established multiverse rumors.
Is Sadie Sink Playing Mayday Parker?
After the news that Sink would be joining Spider-Man 4, folks online were quick to throw out their (typically red-head) fan casts, from Jean Grey to Firestar. It's possible that Sadie Sink is playing a rebooted version of Mary Jane Watson or the MCU's Jean Grey, but what if her true character is related to two previous Marvel legends?
However, one multiverse-jumping idea has gained a lot of interest: Sink is really playing Mayday Parker, the daughter of Tobey Maguire's Peter Parker, and Kirsten Dunst's Mary Jane.
On the surface, this may seem far-fetched, but Maguire was a key part of Marvel's latest Spidey film No Way Home and he confirms that he and MJ are still together in his universe.
It may be a long shot, but many have been quick to point out that Sink could believably play the daughter of the two 2000s Spider-Man stars. In fact, if Mayday Parker were ever brought to live-action, Sink would be the perfect casting.
In Marvel Comics, Mayday Parker is the daughter of Peter and Mary Jane Parker from an alternate future. Inheriting her father's Spider-powers, she adopts the mantle of Spider-Girl and fights crime, despite her parents' initial attempts to protect her from that life. Mayday was recently seen as a baby in Spider-Man: Across the Spider-Verse.
While getting Mayday before Miles Morales in live-action could be head-scratching, here's how her appearance would make perfect sense.
How Mayday Fits into Spider-Man 4
Let's face the facts, following the success of Spider-Man: No Way Home, the next MCU installment could very feature elements of the multiverse.
With Spider-Man 4 releasing between Avengers: Doomsday and Secret Wars, that greatly increases the chances that Tobey Maguire appears. This is because Maguire is heavily rumored to pop up in at least Secret Wars, and Spider-Man 4's plot could be greatly impacted by Doomsday, potentially taking place on Battleworld.
Rumors suggest that Spider-Man 4 may feature multiple villains, with insider reports indicating that both Maguire and Andrew Garfield could reprise their Spider-Man roles, potentially having more screen time than in No Way Home.
With Sink in line for a leading role alongside Holland, part of Peter 2's new story could be bringing Mayday to the MCU. Marvel Studios and Sony have reportedly discussed the multiversal direction, though there were initially disagreements over whether the film should be more grounded.
If Spider-Man 4 turns out to not involve any multiverse elements, Mary Jane would probably be the safest bet for Sink's new character.
Spider-Man 4 swings into theaters on July 31, 2026.
