Neil, who made his debut with "Johnny Gaddar", stars in the titular role as an antagonist in the drama-thriller directed by Bejoy Nambiar.
"Wazir is nothing but dark, he mocks and enjoys somebody else's pain. This is my darkest portrayal yet. I myself was quite shocked that I played this character. He is very unpredictable... Whether it's his face, voice or look, I had to work extremely hard for this," Neil told PTI.
"When the film was offered to me, at that time it was titled 'Ek aur Ek Do'... After I finished shooting, I got a call from Vidhu sir and he said 'What have you done?' I asked him if he was not happy with my performance. He said, 'Happy? I am changing the name of my film to Wazir now.'"
The film tells the story of two unusual friends - a paralysed chess grandmaster, played by megastar Amitabh Bachchan and a grief stricken ATS officer, played by Farhan Akhtar, brought together by a twist of fate.
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"When I got to know that my character would be intimidating Bachchan sir's character, that was scary. His name is itself intimidating so getting on screen trying to intimidate him was not an easy task.
"But, that's where the acting kicks in. I did not want my nervousness to affect his performance so I made sure all the butterflies which were fluttering in the stomach, remained there and never came out on face," he said.
"Wazir" marks Neil's second outing with Nambiar, as the duo previously worked in "David". Neil says he shares a great director-actor tuning with the "Shaitan" helmer.
Even though the actor has played characters with grey shades in movies like "7 Khoon Maaf", "Players" and recently "Prem Ratan Dhan Payo", Neil says he is open to do romantic stories as well.
"I am always attracted to do of characters which are not easy. I would love to do a nice love story. If there is a story that attracts me I would love to do it, like 'New York' which I consider a love story.
"Wazir" is scheduled to release on January 8.