With Marvel’s What If…?, the Disney Plus series has proven to be a bit of a rule-breaker when it comes to pre-established norms of the Marvel Cinematic Universe and lore. While that is understandable for a show whose premise revolves are hypotheticals, Looper has pointed out how the latest episode seems to eschew the precedent set by the comics regarding a restriction of the Infinity Stones’ power.
Namely, in the comics, it has been established a number of times that the stones only hold sway in the native universe they are from. This was established in such works as 2003’s JLA/Avengers comics crossover event, in which Darkseid obtained the Infinity Gauntlet but ended up trashing it after realizing it didn’t work in his own universe. A couple other examples also establish this rule in Jonathan Hickman’s 2018 Fantastic Four run and in Marvel’s The New Avengers.
However, in episode 8 of What If…?, called What If…Ultron Won?, the malevolent android is able to successfully ignite every nuclear bomb on Earth, nearly scrubbing the entire planet from life. Out of boredom, and with the help of the Infinity Stones, he’s also able to enter into alternative universes, does battle with the omnipotent The Watcher, and retains his power in other universes.
This does seem to branch off from the established rules of the Marvel comics, but perhaps these globally powerful Infinity Stones are unique to this one strand of the Multiverse. Either way, we’ll just have to watch and see how the season finale of What If…? pans out when it airs on October 6th, since it was teased near the end of the previous episode that the storyline with Ultron may continue.