Fortnite has featured a whole host of characters from other franchises this year, and there are a number of ways Epic manages to achieve that.
Most games stick to their own cast of characters and when someone or something shows up from another universe or franchise, it's a very big deal and normally an Easter egg that is only ever seen by the most eagle-eyed of players. Unless we're talking about Super Smash Bros., where characters from loads of games meet up to fight each other.
Outside of Smash, Fortnite is the unmitigated king of the crossover. So far in 2019, Fortnite has hosted events including elements and characters from the Marvel Cinematic Universe, John Wick, Star Wars, and Stranger Things. However, how does Epic strike up these deals with such massive franchises? Well, it has managed to do so in a couple of ways.
The biggest collaboration of the ones mentioned above was with Marvel, and it has happened twice. One of the main reasons why the Thanos LTM came to be was due to the fact that Infinity War and Endgame's directors Anthony and Joe Russo are self-confessed fans of Fortnite. The pair played the game a lot while working on the box office blockbusters and jumped at the opportunity to see some of their work become a part of their favorite game.
The John Wick LTM came about in a very different way. Keanu Reeves, who plays Wick, revealed that younger fans were referring to him as "Fortnite Guy." That's because even before the character's LTM, there was a skin that looked a lot like Wick. It's why Reeves loved the idea of actually becoming the Fortnite Guy. At least then when he's called that out in the world, it's actually accurate.
Above all else, the main reason why Marvel, John Wick, Stranger Things, and every other franchise that has made it onto the Island and want to be affiliated with Fortnite is because of its popularity. Millions of people are both watching and playing Fortnite. That's quite the audience to expose your product too. In turn, fans of those franchises might give Fortnite a go if their favorite characters are a part of the game. It's really a mutually beneficial deal for both parties every time a crossover event takes place.