The Marvel Cinematic Universe is a well-oiled machine, one that's constantly introducing new characters. Fans who spent years watching the Marvel movies in order will remember Tom Holland making his debut as Peter Parker/Spider-Man in Captain America: Civil War (which is streaming with a Disney+ subscription). During that first movie, he got some A+ advice about improvising from the one and only Robert Downey Jr.Just like Tony Stark helped guide Peter Parker as a superhero, RDJ had a mentor relationship with Holland IRL. Prior to Spider-Man: Brand New Day breaking records at the box office, the 30-year-old actor spoke in a video from IGN's Instagram about some helpful advice he got from Downey early in his Marvel tenure. In his words: I remember on Civil War I had written down these improvised lines to make me sound smart. And then I was with Downey on set, and I was like, 'You must do this, right? For all the times you chat to J.A.R.V.I.S.?' And he was like 'No. I just make it up.'Well, that was honest. Rather than pretending he was doing specific work regarding all the tech talk in the MCU, the Oscar-winning actor got real and admitted he just makes stuff up when talking to J.A.R.V.I.S. and the rest of Tony Stark's computer assistants. And that no doubt influenced Tom Holland's work in future Marvel movies he'd star in after Civil War. Despite this admission, fans would probably never realize that Robert Downey Jr. was just making stuff up during his countless tech scenes throughout the MCU. That's why they pay him the big bucks, after all. In the same interview, Tom Holland spoke more about the lesson he learned, offering: And I was like 'Oh, wow!' So then I just started practicing. Just practicing being smart. So now I'm like fake smart. Dumb smart. Tony Stark and Peter Parker are both geniuses, so Holland has had to do plenty of wild tech speak throughout the MCU as well. Luckily, RDJ's advice took the pressure off, and now the Odyssey actor is super comfortable with those scenes, even dubbing himself "dumb smart." Just like his mentor, he's pulled it off despite not having the same expertise as his signature character. (Image credit: Sony Pictures, Marvel Studios)I have to wonder if Robert Downey Jr. is going to have to do similar improvisation when he returns to the MCU as Doctor Doom in the next two Avengers movies. He's expected to be playing a very different character in those titles, so maybe he won't have as much tech-based dialogue. What we know about Doomsday is super limited, so fans will have to wait and see how it all goes down this winter.Avengers: Doomsday will hit theaters on December 18th as part of the 2026 movie release list. It's unclear if Spider-Man will end up factoring in, but the Brand New Day credits scene did seem to tease a role in either that blockbuster or Secret Wars. Fingers crossed we get to see Holland and Downey back on screen together.