“What If…?” Episode 8 takes place not long after the events of 2015’s “Avengers: Age of Ultron,” but is set in a timeline where that film’s titular villain has actually won and laid waste to the entire galaxy. Notably, the genocidal AI is able to do that latter feat by killing Thanos and taking control of all six of the Infinity Stones just moments after the Mad Titan’s arrival on Earth.
Victorious and bored, Ultron ends up finding new purpose after he learns about the existence of the multiverse. Reaching a higher level of consciousness, Ultron is able to see and hear The Watcher, and becomes intent on spreading his vision of “peace” throughout the entire multiverse. The episode eventually sees him and The Watcher engaging in a battle that spans entirely different timelines and universes. “The boundaries of the multiverse are irrelevant to beings like you and me,” Ultron tells The Watcher during their fight. “I didn’t evolve by staying inside the lines.”
As some Marvel fans noted on Reddit, the episode makes it explicitly clear that Ultron can use his version of the Infinity Stones outside of their original, home universe. Whether that means every version of the stones that exist in the MCU can do that, or if some (like the Stones featured in the comics) can’t, remains unclear. Either way, it’ll be interesting to see how Ultron’s considerable power stacks up when he inevitably faces whatever superhero team it is that The Watcher begins assembling at the end of “What If…?” Episode 8.