The film starts with the murder of a former Police Commissioner, Shanmuga Sundaram (Subbu Panchu) by an escaped prisoner Kamal Ekambaram (Riyaz Khan). The story then shifts to Masilamani aka Massu (Suriya) and his friend Jet Li aka Jettu (Premgi Amaren) who are small-time con artists. Massu meets Manini (Nayantara), a nurse and they subsequently fall in love. While trying to escape after a heist gone wrong, Massu and Jet meet with a car accident, post which Massu starts seeing dead people, with whom he can communicate. Jettu had died in the accident and is now a ghost, too. Massu forms a group of loitering ghosts to earn money by performing fake exorcisms and extorting money from scared rich people, while promising the ghosts that he would fulfill their last wishes in return. Meanwhile, Manini who thought Massu was working in a finance company gets to know about the fake exorcisms and leaves him in a heist.
One day he meets a ghost called Shakthi (also Suriya), a Sri Lankan Tamil and look-alike of Massu. Shakthi initially seems to help Massu to pull off a large heist. However, he wants to use Massu for his own needs. He sabotages the plan and tricks Massu into running over Anthony (Sharath Lohitashwa), a hawala broker. Corrupt Assistant Commissioner of Police (ACP), Vikram Lakshman (Parthiban) takes charge to investigate the case and finds out that Massu is, somehow involved in the murder. Meanwhile, the ghosts start striking against Massu as they assume that he would cheat them. Massu yells at them and orders them to go out. Just then, Shakti arrives as the ghosts have called him. The ghosts go with Shakthi. But Jettu manages to convince Massu and he agrees to fulfill the wishes of the ghosts. He starts fulfilling the wishes of all the ghosts. He first fulfills the wish of the ghost of a woman, Padma which is to see her son, who is actually blind. Massu is frustrated to learn that he is accidentally responsible for the death of Padma. As a sort of seeking forgiveness, he guides her son, takes care of him and gets his eye operated upon. Her wish fulfilled, Padma attains salvation. This incident moves Massu and he fulfills the wish of every ghost. Meanwhile, Shakthi manages to use Massu to kill another person, Madhivadhanan aka Madhi, an MLA and associate of Anthony. While Massu is furious with Shakthi for having made him a double murderer, Kamal meets Massu and starts telling him Shakthi's past: Massu is Shakthi's son.
Shakthi was a police officer in Quebec City, Canada. He got married to Anuradha aka Anu (Pranitha Subhash), who is a teacher of his daughter Megha's school, just for Megha's wish. Shakthi secretly learns that Anu really loves and takes care of Megha. Anu & Shakthi fall in love. Anu gives birth to a son. Anu owned land in India, which she wanted to donate to an orphanage so that a new orphanage could be built there. Kamal was the only friend of Anu in India and agreed to help with the registration. Sakthi and Anu, along with their little daughter Megha (Yuvina Parthavi) and infant Massu, came to India to complete the registration but get to know that industrialists Radha Krishnan (Samuthirakani) and Anthony forged documents and planned to take the land away to construct flats there. Since Shakthi remained undeterred and did not give way, Radha Krishnan, Anthony and their henchman Madhi and Shanmuga Sundaram, killed Shakthi, Anu and Megha and pinned the murders on Kamal. Massu had escaped because Megha had left him safe in a small house with a family nearby.
Shakthi through Massu wanted to kill all the people who were responsible for his family's demise. Knowing the truth, Massu decides to kill the last person, Radha Krishnan, himself. Radha Krishnan also knows who Massu is and tries to kill him but Kamal saves Massu. However, because he was hit on the head by Radha Krishnan, he loses the ability to see and converse with the spirits anymore. With the help of Vikram, who double-crossed Radha Krishnan, Massu finally kills Radha Krishnan. As Shakthi's last wish is fulfilled, he goes to heaven and joins with Anu and Megha. Manini now reunites with Massu and they get married as Jettu remains with Massu forever.
In early December 2013, Sify reported that Venkat Prabhu's next film after Biriyani (2013) would feature Suriya as the male lead and would also be produced by the actor himself under his newly launched company 2D Entertainment. Three days later the project was confirmed by the director, who however clarified that Studio Green would co-produce it along with 2D Entertainment. Subsequently, lyricist Madhan Karky was signed to write the dialogues for the film. As with Prabhu's earlier films, composer Yuvan Shankar Raja and editor Praveen K. L. were added to the technical crew, while R. D. Rajasekhar was signed as the cinematographer, replacing Prabhu's usual cinematographer Sakthi Saravanan.
The film was touted to be the first Tamil film to be shot in 3D from the beginning, but Venkat Prabhu later informed that it was not true. It was reported to be a horror comedy, while Venkat Prabhu stated that he was "trying something new" and that he could not reveal the genre. The film was rumored to be titled as Poochandi, however Venkat Prabhu announced on 5 July 2014 via Twitter and Facebook that it had been titled Masss. In May 2015, the film was renamed with a Tamil title Massu Engira Masilamani, to be exempted from the State Government's thirty percentage entertainment tax.
Reports in January 2014 indicated that Suriya would be playing a dual role in the film. Further more, he was said to be given two different looks, one of them having him sport long hair. After completing the film, Suriya stated that he had played two characters, Masilamani, a conman, and Shakti. Venkat Prabhu went on to add that Shakti was a Sri Lankan Tamil. Nayantara was signed to play one of the female leads along with Amy Jackson, while the director's brother Premgi Amaren was given a significant supporting role as in all of Prabhu's films. Mohan was reported to be playing the villain, but the director stated that Mohan was not approached for any role in the film. Actor-director R. Parthiepan informed that he had "a special character to essay in Masss, a very significant one". In August 2014, the Times of India reported that Jayaram, who had worked with Venkat Prabhu in Saroja (2008), had been added to the cast and would be playing a prominent role, however, he was replaced by Parthiban. Actors Sriman, Karunas and Daniel Annie Pope of Idharkuthane Aasaipattai Balakumara (2013) fame were reported to be playing the roles of spirits in the film. On 10 August 2014, actress Vidyullekha Raman informed that she would be a part of the project. The next day, actor-director Samuthirakani was announced to be part of the project. Sanjay Bharathi was given a supporting role and participated in the Hyderabad schedule.
In November 2014, Amy Jackson opted out of the project, explaining that the makers had changed her character and the script, which would have resulted in her shooting only for half the number of days than she was initially committed to. She was replaced by Pranitha Subhash who joined the film's cast later the month. In October 2014, Riyaz Khan was named to be a part of the film, and was said to be playing "a very important role with a unique characterization". Prinz stated that he played one of the villains in Masss and that he would appear for a short duration but share screen space with Suriya.
The film was officially launched with a puja on 14 April 2014. Principal photography was reported to start from 11 July 2014, but commenced three days earlier in Chennai. The first schedule was shot in a house on the ECR stretch for 15 days. The crew with Suriya and Nayantara shot some scenes at a hospital in Chennai. The first and second schedules of the film were completed by early September 2014. The team reportedly continued filming in Ooty, Kerala and Kullu-Manali in North India. Forty percent of the filming was completed by the end of September 2014. In November 2014, the first song was filmed, which was choreographed by Ajay Raaj. By early December, the team shot crucial portions including a duet song sequence involving Suriya and Pranitha in Bulgaria. Following the schedule in Bulgaria, filming continued in Puducherry by January 2015.
Yuvan Shankar Raja began working on the film's music in August 2014 and stated that the soundtrack would be "completely wacky". In November 2014, Tanvi Shah had recorded a song for the soundtrack, which was however, not featured in the album. At an award function later that month, the composer told that he was working on a special track that would be a tribute to Michael Jackson and be on the lines of Jackson's "Thriller", later revealed to be "Poochandi". In March 2015, Sify reported that Yuvan Shankar Raja was no longer part of the project and that he had been replaced by S. Thaman as the film's composer. Venkat Prabhu denied the news, and Yuvan Shankar Raja later clarified that, because of time constraints, he composed a tune and gave it to Thaman to work on the orchestration part only, since the team needed to finish the shoot quickly. Thaman had remixed the Bollywood song "Gandi Baat" from the 2013 film R... Rajkumar. The song was included in the film's Telugu version, but not featured in the Tamil album altogether.
Behindwoods rated the soundtrack 3.25 out of 5 and said the songs show " experimentation and vivacity". Indiaglitz gave it 3 out of 5 and said, "To quote YSR, the album is 'completely wacky'. Promise of surprise element – check, tribute to Michael Jackson – check, high energy – check... This album is a reviving, soulful and definitely a chart-topper material". Bollywood Life gave the soundtrack 3 stars out of 5 as well and called it "a crowd-pleasing album".
Thaman had remixed the Bollywood song "Gandi Baat" from the 2013 film R... Rajkumar. The song was included in the film's Telugu version, but not featured in the Tamil album altogether. Although it was separately and officially uploaded in YouTube by Eros Music/Eros Tamil.
The worldwide distribution rights of Masss were sold to Eros International for approximately ₹610 million (US$9.5 million). Dream Factory, a subsidiary of Studio Green was confirmed to distribute the film in Tamil Nadu. Sopnam Films bought the Kerala distribution rights for Masss as well as two other Studio Green productions, Komban and Darling. The rights to Karnataka region were sold to distributor Srikanth. The satellite rights of the film were sold to Sun TV for ₹150 million (US$2.3 million).
The first poster of Masss was released on 22 October 2014, coinciding with the Deepavali festival. The official teaser was released on 25 April 2015 after midnight.
The film was released in around 1900 screens worldwide, including 425 in Tamil Nadu.
Behindwoods gave the film 3 stars out of 5 and said, "It has the expected Venkat Prabhu elements, the crowd-pleasing supernatural factors treated in a slightly different way and of course, Suriya in all his glory." International Business Times also awarded the film 3 stars and said, "One thing obvious throughout the film is the effort taken by the director to make his movie watchable for audience of all age groups. It has romance, some spooky elements, comedy, witty one-liners, action, songs and dance." Oneindia rated it 3 stars as well and wrote, "Thanks to Suriya's brilliant performance and Venkat Prabhu's intriguing story telling ability, Masss will surely be enjoyed by the masses albeit poor VFX hindering the quality of the movie." Indiaglitz gave 3 stars out of 5 too and stated, "Venkat Prabhu has been stereotyped as the director who loves party hard movies, a bit of adult humor and all that, but in Masss he has steered clear of those elements and has given a wholesome family entertainer with an interesting storyline." The Times of India also rated the film 3 out of 5 and added, "The film lacks the raciness of Biriyani or Mankatha, but there is enough inventiveness and joie de vivre to the scenes to keep us entertained."
Sify rated 3.5 out of 5 and described Massu Engira Masilamani as "a no-holds barred entertainer with all the essential ingredients." Rediff gave the film 2.5 stars on a scale of 5 and commented, "There is non-stop excitement, with all the characters in the film being on some kind of high, literally bursting with energy." Deccan Chronicle rated the film 2.5 out of 5 as well, saying that "the film drives up to an intersection where one sign says horror and another, entertainment, and firmly decides on the latter while paying just a passing reference to the former." The Economic Times also gave the film 2.5 stars and wrote, "The paranormal twist in Massu... is what keeps you interested but there are too many twists; some predictable and some good." Writing for The Hindu, Baradwaj Rangan stated, "The idea behind the supernaturally themed Massu is terrific, even it feels like a mashup of many spirit-driven films...the thing with Venkat Prabhu's films these days...(is)...they're all ideas and no follow-through...It's only in the last hour or so that Massu begins to score." Malini Mannath from The New Indian Express wrote, "Not very funny, not very scary, and not very original, Venkat Prabhu's attempt at crafting his first supernatural-comic-vendetta flick, turns out to be a disappointing and a boring affair...The director weaves in a hotchpotch of situations, the screenplay is sloppy and narration is jerky. The characters are one too many and the genuinely appreciative moments are few and far between."
Masss collected ₹5.35 crore on its first day in Tamil Nadu alone, where the collection of next two days were ₹4.90 crore and ₹7.05 crore taking its first weekend gross to ₹17.30 crore in Tamil Nadu and collected nearly ₹3 crore in Kerala on its first weekend. It collected ₹1 crore from Bangalore alone on its first day, the Telugu version Rakshasudu collected nearly ₹5.8 crore on its first two days in AP-Nizam centres. The film grossed around ₹49.5 crore (US$7.7 million) worldwide in its opening weekend, including ₹180 million (US$2.8 million) nett in Tamil Nadu alone with ₹1.84 crore from Chennai alone. From the overseas markets, it reportedly earned ₹160 million (US$2.5 million) in its first three days. The film has grossed approximately ₹87 crore (US$14 million) worldwide from both Tamil and Telugu versions in its lifetime, not adding the entertainment tax in India.
By the end of the box office run, Masss had collected nearly ₹25 crore (US$3.9 million) at the overseas market. Masss was listed as one of the top 10 highest grossing Tamil films of the year.