The #1 on M Countdown on 2012-10-18 was “Bloom” by Gain — win No. 1 for the song and career win No. 1 for Gain (No. 1 on this show).
“Bloom” has 1 music show wins in total: 2012-10-18 M Countdown. Gain had 1 wins in 2012 up to this date, and this was the artist's first win on M Countdown. The previous week's M Countdown #1 was “Crayon” by G-Dragon. Episode data comes from broadcasters' published results (Wikipedia lists, CC BY-SA) and is recounted daily.