The Russo brothers decided to team up with Fortnite to create “Infinity Gauntlet Limited Time Mashup.”

 Avengers: Infinity War directors Joe and Anthony Russo obviously love a good crossover event, but no one saw the Fortnite x Avengers mashup coming. The news of the Fortnite 4.1 adding a new mode called ‘Infinity Gauntlet Limited Time Mashup’ came as a huge shock to everyone, even the developers at Epic Games.The developers at Epic Games explained the “happy accident” on their blog saying, "This collaboration started as a simple phone conversation between Epic and Marvel over a mutual appreciation for Fortnite and Avengers."

This new mode lets players play as Thanos and enjoy some cool new abilities. There was no teaser for the collaboration, no mention in the trailer and no clues, but that's because the developers at Epic Games were not expecting this to happen until the Russo brothers contacted them shortly before the release of the film. They played the game while working on the Avengers: Infinity War and decided to contact Epic Games Creative Director Donald Mustard. They told Entertainment Weekly, "Over the past few months, while we were editing Infinity War, we’d take breaks to hop on and get in a few games [...] And then we started thinking, how cool would it be to have some kind of Avengers–Fortnite mashup? So we stalked Donald."

After Mustard got the call from Joe Russo out of the blue, they quickly started to brainstorm some crazy ideas. “ It was really important that whatever we did, it had to be super authentic to both Fortnite and the Avengers: Infinity War, and something that fans of both would be excited about. About an hour later, we had the bones of this awesome idea for a limited time gameplay mode, and almost immediately our team got started,” Mustard recalled.

Although this collaboration sounds like a great marketing ploy and adding Thanos fits the Season 4 superhero theme perfectly, these two franchises really don’t need to do a crossover for any promotional reasons. The developers explained that "This is a collaborative experiment between friends from start to finish. This kind of opportunity, where you have this mutual respect for someone’s work and you’re on the same page about doing something cool for fans, is rare and really exciting." It seems like this was done purely for the love of each other's work and just because it would be cool, and it totally is.