Marvel withdrawal has been cruel this year. With Captain America: The Winter Soldier and Guardians of the Galaxy released so close to one another last summer, it's now been almost nine months since our last MCU fix, and we couldn't be any more ready for the Avengers' second assembly in Age of Ultron.

Digital Spy visited the set of Joss Whedon's sequel last summer, and spoke to the man himself along with Mark 'Hulk' Ruffalo, Chris 'Thor' Hemsworth, and new recruits Aaron 'Quicksilver' Taylor-Johnson and Elizabeth 'Scarlet Witch' Olsen.Â

Below are 25 of the key things we learned from our day on set.

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1. The Science Bros are causing trouble. "Banner's been living in Stark Tower, and [he and Tony] have been working side by side," Mark Ruffalo shares. "Banner has his own lab now, he's doing work that augments Tony's work, that could lead to a horrible experiment going wrongâ€¦"Â

2. Jeremy Renner's Hawkeye will have a lot more to do this time out. "We got to do some interesting stuff with Hawkeye which is a different kind of dark," Whedon teases. "It's been fun for Jeremy because he was possessed for so long last time â€“ it's interesting to not be a zombie!"

3. We won't see the Avengers assemble again (which hopefully also means we'll be spared a silly alternative UK title). "This movie starts off and the team is together, on a mission, they're working in tandem, and there are new relationships between them," explains producer Jeremy Latcham. "Time has passed, so you pick up right in the middle of an action sequence and start trying to catch up.

"I think that's fun for an audience, to try and figure out, 'Wait, those two are funny together now, there's something going on with them, maybe there's a little tension over there'. You're showing up at a party when it's already a little bit started."

4. One of the key new relationships will be between Bruce Banner and Natasha Romanoff, who already had a close shave in The Avengers when the Hulk almost ripped her apart. "They're an unlikely pair, but there's something about the two of them that neither can deny," says Whedon, while Ruffalo describes them as "kindred spirits".Â

5. "Bigger" and "darker" are two of the most clichÃ©d terms you can apply to a franchise sequel, but Age of Ultron looks set to earn both â€“ according to Ruffalo, it "makes the first Avengers look like Waiting for Guffman".Â

Latcham expands on this by reminding us that much of The Avengers was shot on a small soundstage in Albuquerque, and that its New York City was created "in an old abandoned train station where we'd hung green screen and built part of a bridge."Â

6. Not only are the locations real this time â€“ they're also global. "The Avengers saved New York, but the Avengers aren't just about America," Latcham says. "They're here to protect this blue rock that we all live on."

Hence Age of Ultron's globe-trotting remit, which sees various strands of the gang show up in South Africa, Northern Italy (playing as Eastern Europe) and South Korea among other places. In preparation for one particularly spectacular set piece, producers asked the South Korean government for permission to shut down Seoul's equivalent of the M1 for two weeks. They complied.Â

7. Whedon's favourite character to write is Natasha. "She has a special place in my heart - there is one scene in each movie that was filmed pretty much unchanged from the first draft, and they're both Natasha scenes. She's just somebody that I feel like I get." We're starting the petition for a Whedon-helmed Black Widow movie here, guys.Â

8. New recruits Quicksilver (Aaron Taylor-Johnson) and Scarlet Witch (Elizabeth Olsen) initially join forces with James Spader's Ultron against the Avengers, creating a very different balance of power than solo villain Loki. "Instead of Ultron giving a lot of speeches so everybody knows what he's thinking, it'd be nice if he had some allies," Latcham explains.Â

"The story that Joss put together with these two kids is really sweet and poignant, and you really understand why they would start on this side of the line. It's a great journey that they go on, from being these rough and tumble kids in Eastern Europe who blame the West, and the Avengers for the plight, the power structure of the world that keeps kids like them down. Over the course of it they realise maybe the Avengers are here for good reason."

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9. But the brother-sister duo have legitimate beef with one Avenger in particular. "Our characters have a lot of anger, especially towards Tony Stark, and we want revenge," says Olsen. "We meet Ultron, and he's someone who preaches peace andâ€¦ believes what we believe, which is that the Avengers create destruction and that Tony Stark's bomb is responsible for killing our parents."Â

Unsurprisingly, their alliance with Ultron ends up turning sour, and Olsen reveals that "my character ends up really having to deal with her ignorance. A lot of problems that happen towards the end of the film are her responsibility."

10. As trailers have indicated, there's dissent in the Avengers ranks too. Where the first film saw them begin divided and gradually come together, Age of Ultron begins with them united and gradually tears them apart thanks to Ultron, Quicksilver and Scarlet Witch's divide-and-conquer strategising.Â

(An aside for Buffy fans â€“ to us, the arc of Ultron sounds not unlike that of season four two-parter 'The Yoko Factor' and 'Primeval', when Adam sought to distance the Scoobies from one another before they defeated him by reuniting into one super-being.)

"The larger threat individually isolates each of us," Chris Hemsworth explains. "It's quite a personal kind of threat, and Thor is potentially seeing the bigger picture here - he has a whole other sort of journey for a while, where he kind of goes 'Hang on, this is part of something else, I think'."



11. Much of the Avengers' problem boils down to their lack of a clear leader post-Winter Soldier. "SHIELD has fallen apart, so this movie becomes Tony Stark and Steve Rogers trying to put the Avengers together without a parental unit like Nick Fury hovering over them," explains Latcham. "What you realise is that these are guys who work best with rules, and probably do need some adult supervision."

And as anybody who watched the first film can guess, Tony and Cap aren't an ideal leadership pairing. "Tony has been paying for everything, designing stuff, building new toys, he's the benefactor of the whole thing. But Steve Rogers is very much in charge of operations and missions, he's the moral compass," Latcham goes on. "But how long can Tony Stark have someone else be in charge?" In other words, groundwork is being distinctly laid for the Stark vs Rogers core of Civil War.

12. Making running look interesting on screen â€“ tougher than you think. "The running style we tested early on was just very one-dimensional and boring to look at," Aaron Taylor-Johnson says, "but if you try to do free running, like parkour, then that's very much Captain America's style. Everyone has their thing. You go, 'Can I do this?' No, that's someone else's thing. You have to find your own place in the stunt world."

13. Also tougher than you think â€“ resisting the temptation to accompany your green-screen fight moves with sound effects. "It really sucks," Olsen deadpans. "You have to remember not to do that, you cannot go 'Phtoo, phtoo, phtoo' as you're shooting fireballs."

14. Also tougher than you think â€“ watching yourself in slow motion. "The most painful thing an actor ever gets to do is watch themselves in super slo-mo, while they're doing something strenuous," says Olsen.Â

"That's why when you watch superhero movies everyone has these really calm faces, because it is really horrible to watch someone not have a calm face in slow motion. It's disgusting."

15. Bruce Banner's Hulk-life balance has improved over time, "but it's still evolving," says Ruffalo. "I think he does feel more comfortable with himself and his relationship to Hulk, but that confidence definitely gets shaken during the movie."Â

The team has found a way to strategically deploy the Hulk, holding him back as a last resort "nuclear option" who doesn't get involved with fights unless absolutely necessary. "He's sort of left behind in waiting as the secret weapon, the nuclear bomb."

16. Though a Hulk solo movie is nowhere to be seen on Marvel's upcoming slate, there's a lot of ground Ruffalo wants to see covered with 'the other guy'.

"I feel like we haven't even scratched the surface with Hulk, as far as his character goes. The technology just hasn't completely been available, and I think we've sort of been ignorant about the approach, like, what can we do with the Hulk? Yeah, he's great and it's exciting when he freaks out and smashes, but there's a whole character there from the comics, who can talk and has a personality.Â

"Is it always just rage? I think there's a battle of identity going on between him and Banner, about establishing dominance, and what troubles Hulk in a very primal way is Banner, because he's the only thing that has any control over him. That sets up an interesting dynamic that hasn't been explored yet."Â

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17. As has been widely publicised, Age of Ultron's portrayal of Quicksilver and Scarlet Witch is under strict limitations thanks to the messy split rights between Marvel and Fox. For one, they can't be called mutants, and for another their backstory can't be true to the comics, according to Olsen. Both actors nonetheless used the comics for inspiration.Â

From the looks of it, the pair are brought into the Avengers fold by Hawkeye, after initially joining forces with James Spader's villainous Ultron. Taylor-Johnson and Olsen both kicked off filming with several days alongside Renner in Aosta, Italy, which is being played as their Eastern European homeland.Â

18. Whedon and his cast have developed a system for controlled improv. "Joss is such a writer that he'll have ten alternatives written, if there's a joke and he's worried Downey's not gonna like the joke," says Latcham.Â

"Downey always comes in with a couple of alternatives, so there's definitely room for interplay, but with a cast this big you want to make sure you stay on point. You don't want to let the scene wander off into something we all find hilarious on the day, and later in the editing room makes you go, 'Arrgh, what are we doing?'

"Sometimes when everyone gets together, they're all so funny that they kind of slip out of character, and start saying stuff that's not quite in line with what their character would say. Joss is really great at moderating that on the day, keeping his eye on the big picture."

19. There will be some emotional follow-through from recent solo films â€“ including Steve's search for Bucky â€“ but it's a tightrope walk for Whedon. "We have to honour all of that, and also ignore it, because not only can Steve not be busy looking for Bucky in this film, but he shouldn't make any kind of progress on that at all.

"Some people don't see this, they only want to see the Captain America movies. In comic books, if you do a big crossover event, back in the old days the solo books would just carry on. Now it's sort of like if you buy one, you have to buy them all, and I never want to do that. I don't want to make a movie where you have to have seen the other movies. So it comes up, because we have to respect what they've all been through, but this film is a simultaneous side-bar."Â

20. On a similar note, Hemsworth found it strange not to be working closely with Tom Hiddleston for the first time. "I was interested to see what was gonna be his conflict or his motivation, because he was sort of driven by that relationship previously. I love working with Tom, and I think there's always room for more Thor and Loki stuff, but it's nice to do something completely different."

21. Ruffalo intriguingly describes Ultron as "a perfect reflection of [The Avengers] themselves".

22. This is the first true-blue superhero movie Marvel has done in a long time. "With Winter Soldier we said, 'Let's make a 1970s paranoid thriller', with The Dark World we said, 'Let's make a full-blown fantasy film', and with Guardians we said, 'Let's make a full-blown space opera'," Latcham says. "Everything else has been kind of its own genre, so from our perspective if we can keep changing what this kind of movie is, and saying you can't pin down a Marvel Studios film... then people won't get bored."



23. That being said, Whedon found himself categorising Age of Ultron in just about every genre under the sun throughout production. "With the first one, I set out to make a war movie. This time I said to Marvel, 'I really want to make more of a science-fiction horror', but then in the first week I was like 'This is clearly a western'.

"Then it became a war movie again, then oh no, it's a romantic comedy, a 1940s romantic comedyâ€¦ No, it's Ibsen! No, okay, it's definitely an adventure. It's an action comedy! I suppose if it's gonna get put in a category, it has got some science fiction in it, but for me, it's just everything. And hopefully that doesn't come out as ADD, but as what happens when you put these different people together, you get that kind of weird dissonance with their different worlds and styles, and you hopefully make music out of it, instead of a horrible cacophony."

24. And in case you were wondering, Whedon is even less likely to direct an Avengers/Guardians crossover than he is to return for The Avengers: Infinity War. "I cannot imagine directing a film with â€“ if you'll pardon the expression â€“ more f**king people in it. I'd love to see one, though."Â

25. Between takes, the cast share exactly the kind of conversations you want to believe they do. "Just last week," Hemsworth recalls, "I was talking to Lizzie [Olsen] and I was like, 'So what exactly are your powers?' And she's like, 'Oh, I can manipulate matter and get inside people's heads, what about you?' 'Oh, I've got a magic hammer and I can fly.' What a ridiculous conversation!"

The Avengers: Age of Ultron is released on April 24 in the UK and May 1 in the US.Â Watch behind-the-scenes footage below:

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