King of Masked Singer is a singing competition program presented by Kim Sung-joo, with introductions by voice actor Lee Won-joon. It airs on MBC on Sunday at 16:50 (KST) which started airing from April 5, 2015 as a part of MBC's Sunday Night programming.
Each competition lasts for two episodes, with the singers competing one-on-one in three elimination rounds. They are given elaborate masks which are made by designer Hwang Jae-geun to wear in order to conceal their identity, thus removing factors such as popularity, career and age that could lead to prejudiced voting. In the first round, both contestants sing the same song, while in the second and third round they each sing a solo song. The winners of each pair are selected by the audience and panel of celebrities through instant live votes. The identities of the singers are not revealed until they have been eliminated. The winner of the third round challenges the previous competition's Mask King, and is either eliminated or becomes the new Mask King. Ha Hyun Woo of Guckkasten ("Music Captain") has nine consecutive wins, which is the highest number of wins achieved by any contestant.
SOURCE: MBCKpop | Wiki
My favorites would have to be his versions of "Fantastic Baby" (at 15:48 mark) and "Waiting Everyday" (at 39:06 mark). He shared in one of his interviews that his strategy was to alternate fast and slow songs every time he performs. I really want to kick myself of missing out on the opportunity to watch Guckkasten live when they came to our country.