Avengers: Endgame was the most climactic film in the Marvel Cinematic Universe. It was the culmination of two decades of storytelling and universe-building, jam-packed into a trip down memory lane. In addition to a fantastic final battle against Thanos, Endgame included a plethora of memorable moments — Sam’s “on your left,” Captain America wielding Mjolnir, and Tony Stark’s “I am Iron Man” all stand out. However, the best moment from the film was actually improvised by an actor.
In Infinity War, Doctor Strange saw 14,000,605 possible futures following Thanos’ collection of the Infinity Stones. This revelation played a major role in the sorcerer’s decision to hand over the Time Stone to the Mad Titan, a choice Tony was very angry about afterwards. He didn’t understand the reasons behind Doctor Strange’s actions until the final act of Endgame.
In the battle against Thanos, the Avengers assembled all of their allies and charged the Mad Titan and his army. In a bid to keep the Infinity Gauntlet out of Thanos’ hands, Tony Stark saw an opportunity to seize it, but not before meeting eyes with Doctor Strange in a moment of quiet understanding. In the midst of the chaos, the magician held up one shaky finger to Iron Man, indicating that this was his one shot to defeat Thanos. This emotionally resonant moment cleary laid bare the the stakes of the fight, and Tony’s sacrifice may have felt a lot less poignant without it.
As it turns out, Benedict Cumberbatch improvised that pivotal moment. Doctor Strange director Scott Derrickson revealed as much on Twitter. Derrickson didn't add any further information, but the revelation that Cumberbatch would hold up a finger unprompted is not a surprising one. Robert Downey Jr. also improvised his “I am Iron Man” line, and “I love you 3000” was inspired by the actor’s children. It’s hard to imagine that Endgame — a film planned well in advance and heavily reliant on on CGI and special effects — would allow so much ad-libbing by its actors.
However, it seems that Anthony and Joe Russo are open to allowing their actors some freedom to add in lines or moments that were otherwise not written in. It’s a trend that has worked in the MCU films’ favor. For example, in Infinity War, Spider-Man’s final lines before being dusted are improvised by Tom Holland and this was actually encouraged by the Russos. Other famous improvisations have been done throughout the other MCU films, and it stands to reason that the most unscripted moments are the ones that feel all the more special.
Avengers: Endgame is currently streaming on Disney+.