Spider-Man: Brand New Day, the final Marvel film before Avengers: Doomsday, may have quietly introduced technology that fuels the villains of the December instalment. In the film, Peter Parker (Tom Holland) develops a power-suppressing inhibitor, inspired by Bruce Banner's Hulk-control device, to manage his own mutating spider abilities and to subdue the telepathic mutant Jean Grey (Sadie Sink). The US Department of Damage Control subsequently seizes this technology, raising the possibility that it could be used to build Sentinels, the mutant-hunting robots already glimpsed under Doctor Doom's command in Avengers: Doomsday trailers.

Damage Control uses Peter's inhibitor to restrain Jean Grey while scanning her brain to study and potentially replicate her telepathic powers, after she injures the organisation's leader by unleashing the Hulk in their facility. Sentinels are traditionally built by frightened humans to suppress mutants, and given the fear Damage Control has already shown, the article suggests they could use Peter's tech and data gathered from Jean and her sister Sara to construct their own. This links to the returning X-Men: Days of Future Past cast and suggests Peter's well-intentioned but short-sighted invention, much like his memory-wipe request in No Way Home, could have far-reaching consequences for the MCU and the upcoming X-Men film in 2028.