Christopher Markus and Stephen McFeely have been a screenwriting team for quite some time, and when they landed the job writing Avengers: Infinity War, it instantly became the biggest project of their careers in every sense of the word. No really, it's a nightmare to try and coordinate all of these characters, how they'll enter the film, how they'll exit the film, and everything in between. I don't envy them one bit.
While speaking with Cinema Blend (link below), they discussed their process of gathering information on the characters coming into the film from other franchises and how difficult it is to complete a screenplay with this many intangibles involved...
Stephen McFeely: Some of it is informed guesswork. Some of it is constantly pestering people who are making those [other] movies to tell us what they’re doing. And sometimes it is us going, ‘It would be massively beneficial if this person could be in this place at the end of your movie. I don’t care what he does in your movie, but by the end of it…’
Christopher Markus: And you know, we write it, we assume when we write it and rewrite it and rewrite it, as more information comes in, we will be adjusting. When we’re turning in the first draft, it’s absolutely that, a first draft, and we’ll go through a lot before we get to November.
I can't even imagine the clusterfuck this script writing process has got to be. I mean, there's only so much information you're privy to as a writer, so this has got to be daunting. Godspeed fellas.
Via Cinema Blend