"Monster" is a song recorded by Red Velvet - Irene & Seulgi, the first sub-unit of South Korean girl group Red Velvet, for their 2020 eponymous debut extended play. A dance-pop track with influence from dubstep genre, the song was written by songwriter Kenzie, while production was handled by Yaakov 'Yash' Gruzman, Jenson Vaughn, Delaney Jane and Yoo Young-jin. It was released on July 6, 2020 by SM Entertainment and Dreamus, serving as the lead single from their first major release. Music video The music video for the song was scheduled to be released with the song on July 6 but it was delayed and eventually released the next day. On June 4, 2021, the music video for the track reached 100 million views on YouTube. Commercial performance "Monster" debuted at number 8 on the South Korean Gaon Digital Chart, becoming the duo's first top 10 hit. It debuted atop the Download chart for the period July 5—11, 2020 and peaked at number 13 on the component Streaming Chart. The song entered the Billboard K-Pop 100 at number 28 on the chart issue dated July 11, 2020. It peaked at number three in the following week. The track appeared as the 157th biggest hit single on 2020's Gaon Year-End Digital Chart. In Malaysia, "Monster" debuted at 16, and peaked at eight. The song debuted at number 30 on the New Zealand Hot Singles Chart. In Singapore, the track debuted at 18 on the Streaming Chart, and peaked at five. The song also debuted at number six on the Regional Chart, and peaked at two. On the Billboard World Digital Song Sales chart, the track debuted and peaked at number seven becoming the duo's first top 10 hit on the chart. Critical reception Following its initial release, "Monster" was met with mixed to positive reviews from music critics. Rania Aniftos of Billboard magazine described the track as "bold", further praising Irene and Seulgi for "preaching their confident individuality, and the "monster" inside as they deliver sultry choreography weaved in with eerie, paranormal scenery.". Writer Riddhi Chakraborty of Rolling Stone India described the song as "one of the most stand-out singles of the year" referring to the subunit's "fascinating use of dark pop and dubstep". On another song review, writers Kim Sung-hwan, Yeol Shim-hi, Yoo Seong-eun, and Cha Yoo-jung of Y-Magazine described the track as "well-organized, from narratives reminiscent of delicate horror