The group released their digital single and music video for ‘Who’s That Girl’ on October 4, 2012 and started promotion on October 5 on music program Music Bank. A few days on October 12 the dance practice video for ‘Who’s That Girl’ was released.
On January 20, 2013 on the official YouTube page a teaser was released for the group’s second single ‘Highway’. The single and music video for the song was released on the 24th. “Highway” is produced by Brian Kierulf & Joshua Michael Schwartz, the same producers who created the group’s debut track “Who’s That Girl”. They started their comeback promotions on M! Countdown the same day.
On June 25 the group updated their official fan cafe with a teaser photo. In addition to photos of the members, the teaser announced that Mr.Mr will pre-release its title song on July 5 followed by first mini-album release on the 8th. On June 30 the first teaser for the group title song ‘Waiting For You’ was released. The music video was released on the 4th of July, 2013 the mini album for their first mini album was released on the 5th.
On November 8, 2013, it was announced that new member, Hon, would be joining the group as the sixth member. A music video teaser for Hon was released on their official YouTube account revealing that the group will be making a comeback with their 3rd digital single on November 8, 2013. On November 5, 2013 the album jacket photos of each members along with a group photo were released. On November 6, the second teaser for their comeback was released for their third single ‘Do You Feel Me’ the song and music video were released on 8 November 2013 they starting comeback promotion of the single the following day on music program Music Bank.
On December 7, 2013 the group released their first episode of their reality show ‘MMTV’.