Director Joss Whedon has admitted shoehorning a slew of superheroes into the new Avengers movie was a “nightmare”, as the latest trailer for upcoming sequel Age of Ultron hits the web.

Speaking to SFX magazine, Whedon said getting newcomers Scarlet Witch, Quicksilver, Vision and evil robot menace Ultron himself to sit pretty alongside established characters Iron Man, the Hulk, Thor, Black Widow and Captain America was “the hardest juggling act I have ever, ever tried to pull off”.

He added: “They’re very disparate characters. The joy of the Avengers is they really don’t belong in the same room. It’s not like the X-Men, who are all tortured by the same thing and have similar costumes. These guys are just all over the place. And so it’s tough. Honestly, this is as tough as anything I’ve ever done, and I haven’t worked this hard since I had three shows on the air.”

Whedon did reveal that Mark Ruffalo’s hugely popular Hulk gets a bigger part in the sequel, and said he hoped to add a realistic documentary-style veneer this time around.

“There is more Hulk in this movie than there was in the last film,” he said. “But what I’m excited about is we shot this movie very differently. I was running a lot of cameras, I was shooting long lenses, which I don’t usually do.

“What I love is we have the opportunity, because we went in with this mission statement, to shoot the Hulk like a character in a movie, and not like a ‘Look what we’ve got!’ We have ‘overs’ – blurry ‘Hulk’s over there!’ bits, very quick shots. Everything isn’t, ‘We built the Hulk so for God’s sake you’re going to watch him in this long take, full-frame, the whole time!’ We really got to make him one of the characters in the movie. And that was a gift.”

The new trailer for Age of Ultron was unlocked on Wednesday by fans using the hashtag #avengersassemble on social media. It shows Aaron Taylor-Johnson’s Quicksilver and Elizabeth Olsen’s Scarlet Witch encountering Ultron in what may be an early scene, and also features Robert Downey Jr’s Tony Stark/Iron Man lamenting his role in the nefarious machine intelligence’s creation. The Hulk and Iron Man are once again shown smashing up a major metropolis (with the latter in the Hulkbuster armour), and there’s a final shot of Paul Bettany’s the Vision as the trailer fades out.

Avengers: Age of Ultron hits cinemas on 23 April in the UK and May 1 in the US.