On this episode, guests and MCs were given the mission to call up their close celebrity friends and persuade them to visit them without letting them know that they're filming for the show. 

For the mission, MC Park Myung Soo invited IU, who he previously collaborated with on 'Infinty Challenge'. The singer seemed confused at first at Park Myung Soo's sudden request but ultimately showed up and even brought spicy rice cakes (ddeokbokki) for Park Myung Soo.  

SEE ALSO: IU reflects on her 100th concert and the end of her world tour

IU appeared casually dressed in a white hoodie and a black cap, saying, "I did put on a little bit of makeup. Yoo In Na unnie suggested it."  She added, "Park Myung Soo sunbae doesn't usually call me this late in the night. I didn't know you guys were recording 'Happy Together 3.'"

Upon request, IU sang her latest track "Night Letter" brightening up the studio.