There are things that are not explained in What If …?, The Marvel Studios anthology series. The new Ultron just became the first MCU villain to effortlessly travel across the multiverse. How does this make sense if the Infinity Stones are nothing more than paperweights in transit to alternate lines, as we have seen at the AVT offices in Loki?
Episode 8 explored a scenario where the Avengers were unable to prevent Ultron from achieving his goal and taking control of Vision’s body. In the main MCU timeline, Vision was meant to be Ultron’s weapon, but the Avengers prevented this from happening and transformed him into a hero by charging him with Tony Stark’s JARVIS AI.
Shortly after discovering Uatu’s existence, Ultron broke into the Watcher’s private dimension and then traversed an untold number of alternate universes during their fight. This can likely be attributed to the Space Stone, which allows the user to travel anywhere in the universe they wish.
It could be that the energy provided by the Reality Stone or the Power Stone (or possibly all of them) gave Ultron the means to break the boundaries of his own timeline, which is presumably a bit beyond what the Space Stone can do on your own.
MARVEL | Best scenes from episode 8
What this means is that when one has all six Infinity Stones, it is not just one universe that is in danger. One character who can unite all six is essentially a threat to the entire multiverse, as they can jump from one timeline to another with very little effort. Additionally, they can view and enter dimensions that should be off limits, which was made clear by the scene where Ultron invaded the Watcher’s hidden domain.
