Jennifer Lawrence "struggled" with Mystique's darker side.
The 23-year-old actress plays the villainous, blue-hued mutant shapeshifter in 'X-Men: Days of Future Past' and she often contemplated going off-script for the darker scenes.
She said: "I was struggling back and forth with wanting to get darker ... There was one scene where I couldn't get past thinking she'd shoot someone where she doesn't in the script. We filmed it both ways, but I don't know which one they'll use."
The actress also gushed about her time working with director Bryan Singer and was delighted when she found out he was going to helm the project.
Quizzed on working with Singer, she told Total Film magazine: "It was amazing! There was a tiny fan boy inside of me jumping up and down and screaming when he decided to direct."
Talking about Singer sharing the experience with fans on Twitter, Lawrence added: "He took pictures of everything. He always had his phone out. He was like a 13-year-old girl at a premiere."

Jason Orange has been flirting with Les Dawson's daughter.
The 'Greatest Day' singer met Charlotte - the 21-year-old offspring of the late comedian - at Manchester bar and although she didn't realise who he was at first, the pair "quickly hit it off".
A source told the Sunday Mirror newspaper: "Jason and Charlotte got chatting Neighbourhood on a Sunday evening and quickly hit it off - even though she wasn't totally sure who he was."
Charlotte and the 43-year-old star got on well, and it is said the pair have since "had another chat on the phone".
The insider added: "She did think he was quite a lot older than her, but he was charming and funny and they chatted for ages before he gave her his number and made it quite clear he'd like to take her out.
"He certainly seemed pretty keen and Charlotte's a gorgeous girl, but she's been quite coy about it since.
"They've definitely had another chat on the phone so who knows what will happen?"
Charlotte's father Les - a legendary entertainer - passed away in 1993, and Jason's Take That bandmate Gary Barlow often pays tribute to him during live shows.

Harry Styles still gets starstruck when he meets other celebrities.
The One Direction singer is in one of the biggest bands in the world, but he still has to "take a step back" whenever he comes face to face with his heroes.
Speaking at an event for cancer-care charity Trekstock, he said: "There are always times when you meet someone or talk to someone and you take a step back and think, 'This is the weirdest thing that's ever happened to me.' "
Despite the group's global fame - which has been compared to the fanatical following of The Beatles in their heyday - the 'Story of My Life' hitmaker has previously admitted they aren't on the same level "in terms of music".
He insisted: "We all sat and watched the film of [The Beatles] arriving in America. And, to be honest, that really was like us.
"Stepping off the plane, the girls, the madness. It was exactly the same as when we got there - just 50 years earlier.
"But none of us think we're in the same league as them music-wise. We'd be total fools if we did. Fame-wise, it's probably even bigger, but we don't stand anywhere near them in terms of music."

Russell Crowe "was devastated" when he heard of Philip Seymour Hoffman's death.
The 'Noah' star revealed he regrets never getting to work with the late actor - who died from a drug overdose last month - and paid tribute to his "good friend".
He told the Mail On Sunday newspaper's Event magazine: "We never worked together and I would have loved to.
"He was a great bloke. We got along so well. Like everybody else I was devastated when I heard of his passing. He was a good friend."
Russell also opened up about aging and admitted he won't be celebrating his 50th birthday next month, saying he stopped enjoying the occasion once he turned 48.
He added: "You know, I was happy with every birthday up until I turned 48.
"For some reason there was something about 48 that I thought, 'Oh f**k that! I've gone beyond the pale'. It didn't sound like a happy age."
Now a proud father - with sons Charlie, 11, and Tennyson, seven, with ex-wife Danielle - the actor revealed the impact religion has had on his life.
He said: "I went to Sunday School and when I was older, I went to different churches - Anglican, Presbyterian, Catholic, I explored it all.
"I've had one of my boys baptised, Charlie, and we'll have Tennyson baptised in the future."

Dannii Minogue and her sister Kylie are "more boring than people think".
The fashion designer admitted her wild days are behind her, but she and her older sibling still enjoy a quiet night in "curled up on the couch watching TV".
Speaking to The Sun on Sunday newspaper's Fabulous magazine, she said: "Kylie and I are so much more boring than people think. When we have time together, it's down time.
"We're usually curled up on the couch watching TV or making a cuppa. It's boring Nannas-ville."
Part of the reason for the pair not heading out as much any more is due to fans and the general public staring at them if they're spotted out and about.
She admitted "We don't really go out-out that much because people spend the whole time [staring].
"It's weird. So we just normally eat at home. She loves it when I cook, but she's a really good cook too - even though she doesn't think she is."
Dannii also hinted at her romance with producer Adrian Newman, saying she is "happy", but refusing to give any more details.
She added: "I don't want to talk about any relationship stuff, but I'm happy and life is good. There's not much more to say."

Sir Tom Jones wants to convince Kylie Minogue to remain in her role as a coach on 'The Voice'.
The 73-year-old singer admitted he hopes his fellow mentor will sign on for the next series, and insisted the show should keep the same judging panel for another year because "it feels good".
According to The Sun on Sunday newspaper, he said: "The show is working now. Everybody seems to like the line-up so why spoil it? Why change it if it's working and it feels good?
"I don't know what the commitments are that Kylie has but I'd try to persuade her to stay on.
"Kylie and Ricky [Wilson] are being themselves and this combination works - that's the main thing."
The 'I Should Be So Lucky' hitmaker has revealed her touring schedule means she won't be able to return despite enjoying her time on the show so far.
She explained: "I'm touring later this year and the timings wouldn't work.
"We started filming in November last year and I'm on tour in September, October and November this year ... I have loved doing the show although there have been parts that have been really emotional."

Jeremy Kyle is set for his own celebrity chat show.
The TV presenter - who hosts his own programme in which he helps members of the public resolve their personal issues - is in line to expand his presence on daytime TV with a more prominent role.
An insider told the Sunday Mirror newspaper: "It will have a similar feel to 'Piers Morgan Life Stories' and will explore the troubled pasts of celebrities ... Everyone is tremendously excited that Jeremy's role is expanding.
"He is a huge asset to the channel and the viewers love him. He's very talented and fans will be pleased to see a lot more of him and bosses are confident his new role with strengthen the daytime schedule."
The new programme won't impact on his current show, with plans for it to air at 2pm following 'The Jeremy Kyle Show' at 9.25am.
A spokesman for ITV confirmed: "A series of Jeremy Kyle celebrity special shows will air later this year in an afternoon slot alongside his successful morning show."
The star will begin filming for the five-part series next month.

Julia Roberts' children are her priority over her acting career.
The 'Pretty Woman' actress - who has nine-year-old twins Hazel and Phinnaeus and six-year-old Henry with her husband Daniel Moder - only accepts one movie role a year so she can spend most of her time with her family.
She explained: "I make one film per year and that's a good balance. My older kids have just turned nine and my son is six; they still need me. My family takes up a lot of my time and my creative energy, but I'm lucky to have worked enough already to allow myself to take time off.
"When I see my friends struggling to juggle both, I feel very privileged. I act less, but better; I've always been demanding [of a role], now I'm difficult."
Julia, 46, insists her family life is just like every other and she worries about little things like her kids finishing their homework in time.
Quizzed about her household, she said: "[It's] the same as every other stay at home mom. Sometimes, there are wet bath towels strewn all over the house, dinner isn't ready and the kids haven't finished their homework..."
The 'August: Osage County' star claims showbiz has changed since her 90s heyday and is amazed by today's young actresses who manage to cope with the pressure.
She told France's ELLE magazine: "When I started out, you were allowed to start off slowly. You would do a film and for the next one, you would be given more responsibility and more money, you had the time to figure out what was happening to you.
"These days, you're catapulted into the arena. The web has brought with it a culture of meanness. It's become too easy to propagate rumours and to gossip. It's very difficult for young actors."

L'Wren Scott "didn't want the shame of being poor", according to her ex-housekeeper.
Lupe Montufar worked for the late fashion designer - who was found hanged in her Manhattan apartment on Monday (17.03.14) - for 16 years, and claimed she lived beyond her means and "had a lot of money problems".
She told The Sun on Sunday newspaper: "She didn't want the shame of being poor and all the doors of her rich and famous friends shutting in her face ... She had a lot of money problems.
"She would spend, spend, spend. She would do a job, be paid £15,000 and spend all the money at the shops on herself - and not pay staff.
"She went shopping almost every day. She would spend £350 on a bra. She would buy clothes and then never wear them."
Lupe also claimed L'Wren's partner Sir Mick Jagger initially helped her with her financial problems before deciding to stop just giving her money for things she didn't need.
She added: "Mick would help her out with the money and her business but I think he eventually told her to deal with her problems.
"L'Wren would try and put things on Mick's account without him noticing.
"Mick would tell his assistant to check and make sure he wasn't paying for L'Wren's things. He was happy to pay for their food and things like that. But he wouldn't just give her cash."

Kelly Osbourne wants to stay single for a really long time.
The 29-year-old star - who broke off her engagement to Matthew Mosshart in January - said she is "really enjoying" her life as it is, and has no idea if she wants to settle down and "get married" in the future.
She told the Mail on Sunday newspaper's You magazine: "I plan on being single for a very, very long time. No, I don't think it's possible for someone to sweep me off my feet right now.
"I'm really enjoying my life ... I don't now if I will ever get married. I think my views on marriage are changing as I get older - not out of heartache, it's just that the world is changing.
"But if I ever do get married, I'm never changing my last name."
Kelly insisted she would "be a good mum", although having seen "how much work" her brother Jack puts in with his daughter Pearl, she knows she isn't ready for such a commitment just yet.
She added: "I think I'd be a good mum. But I see with Pearl how much work it is and how you have to be hands-on at all times.
"One minute she's there and then, all of sudden, you think, 'Where the hell has she gone?' It's a big responsibility. I am not ready for that yet."

Tina Fey was "nervous" about kissing Kermit the Frog in 'Muppets Most Wanted'.
The comic writer and actress has a smooch with the Muppets puppet in their latest film, and joked that he was a perfect gentleman about it.
She told Us Weekly magazine: "I was nervous but Kermit put me at ease. Although I did hallucinate for a few hours afterwards."
Tina's comments about hallucinating are a joking reference to the Bufo Alvarius variety of toad - commonly known as a Colorado River toad or Sonoran Desert toad - which when stroked under its chin produces a poison which can be hallucinogenic if consumed by humans.
Speaking about her role as a bad guy in the film, Tina added her daughters Alice, eight, and Penelope, two "are excited to see the movie."
Tina famously wrote and appeared in catty high-school comedy 'Mean Girls' and while she has ruled out a sequel, she's keen for there to be a ten-year anniversary of some kind.
She has said: "[There's] definitely not a movie. It's just the anniversary is coming up, so everybody get your pink shirts. It's been 10 years. You can tell when you look at me it's been 10 years."

Sarah Harding has wanted to launch a solo career for a "long time".
The 32-year-old star was catapulted to the spotlight alongside Cheryl Cole, Nadine Coyle, Nicola Roberts and Kimberley Walsh in Girls Aloud and since the band split last year the blonde beauty thinks it's the "right time" for her forge her own legacy in the music industry.
Quizzed on whether it's daunting going solo, she said: "Yeah of course! But it something that I have wanted to do for a long time and I think now is the right time (hopefully!). "
Sarah - who is performing a showcase gig at the O2 Academy Islington, north London on March 26 - will miss the "banter" she shared with her former bandmates and the support they gave each other during performances.
She added in an interview with BANG Showbiz: "[I will miss] being part of a team and having them there to back you up on stage and the banter! "
The star is working on penning tracks and is excited about getting her teeth into aspects of the music industry which she wasn't able to explore during her time in the band.
Sarah added: "I think so! I'm doing a lot more writing now. Whilst in the group I didn't get much chance."