Prior to the release of Avengers: Infinity War, screenwriters Christopher Markus and Stephen McFeely revealed that each Infinity Stone that Thanos came to possess would have some cost attached, and now they've revealed there was a physical price for using all six Infinity Stones at the same time.
In an interview with Collider, Markus and McFeely were asked if Thanos paid a physical price for using all of the stones at once. "That’s an immense amount of energy," Markus replied. "There’s a reason why other people haven’t done this. Because I think it’ll kill you. So the strongest guy in the universe has to be the one to do it. And I don’t think he’ll be doing much with that arm."
In Avengers: Infinity War, Thanos performs the deadly finger-snap using all six Infinity Stones after Thor drives Stormbreaker into his chest. Thanos is then transported to an ethereal plane inside the Soul Stone where he has a vision of a young Gamora, who asks him if he did it and what did it cost, to which Thanos responded, "Everything."
When Thanos returns from the ethereal plane, the Gauntlet is completely mangled, smoking and blackened, damaging his left arm dramatically. According to Markus, the damage caused by the Gauntlet is severe enough to significantly limit his ability to use his left arm. Thanos paid a steep price for accomplishing his goal to wipe out half of humanity, losing the Black Order, his favorite daughter Gamora and the use of his left arm in the process. We'll have to wait and see if Avengers 4 follows up on this new development regarding Thanos' damaged arm.
In theaters now, Avengers: Infinity War is directed by Joe and Anthony Russo and stars Robert Downey Jr., Chris Evans, Chris Hemsworth, Mark Ruffalo, Jeremy Renner, Scarlett Johansson, Paul Bettany, Anthony Mackie, Paul Rudd, Elizabeth Olsen, Tom Holland, Benedict Cumberbatch, Chadwick Boseman, Chris Pratt, Zoe Saldana, Dave Bautista, Bradley Cooper, Vin Diesel, Tom Hiddleston and Josh Brolin, among others.