RBB (EP)

Following the group's promotion with their second "special summer" release Summer Magic in August 2018, news about Red Velvet's upcoming comeback circulated in October 2018, which was later confirmed by SM Entertainment.^[3][4] On November 9, 2018, SM Entertainment revealed the details of the extended play, its eponymous lead single, titled "RBB (Really Bad Boy)", and the release date to be November 30.^[5] During a V Live broadcast, member Yeri stated that the preparation for the album was longer than their other title tracks.^[6] In contrast to their previous release schedule, the album was released on Friday, November 30 rather than the usual Monday release for most K-pop acts. The release was a singular version only, containing a CD, a photo booklet, a lyric book and collectibles.^[7]

The lead single "RBB (Really Bad Boy)" was characterized as an R&B pop dance track with a catchy melody. The song was written and composed by SM Entertainment songwriter Kenzie and co-composed by Timothy 'Bos' Bullock, Sara Forsberg, MZMC with arrangement by Bullock. Lyrically, it expresses the charms of a "bad boy".^[8][9]

The second song "Butterflies" was described as a punk-pop track, its lyrics comparing the sensation of falling in love to a butterfly dancing. "So Good" was characterized as a future bass track with an R&B base that features a piano melody and rhythmical drums in the instrumental. "Sassy Me" is an urban pop dance track that ranges from low to high notes that allow the group to show off their vocal ability. "Taste" is an old-school dance-pop song with lyrics that talk about the choices a person makes and not listening to others' opinions, following their heart instead. It features a narration written by member Wendy.^[10]

To promote the album, Red Velvet held a V Live broadcast on November 29, the night before its release.^[6] The group had their "comeback stage" for RBB on the music program Music Bank, performing both the title track "RBB (Really Bad Boy)" and "Butterflies" live for the first time and an hour before the album's official release.^[11] This was followed by performances on Show! Music Core and Inkigayo.^[12]

An accompanying music video for "RBB (Really Bad Boy)" with choreography by Choi Sun Hee, Kaycee Rice and Janelle Ginestra was released on the day of the album's release.^[13] The Halloween-themed video, which had a "Howliwood" sign in the background (a parody of "Hollywood") featured the titular "bad boy" in the song in the form of a werewolf who chases after the girls throughout the video, moving from various retro-inspired sets such as a pink room with a checker-patterned floor, a pumpkin patch with the sign behind it, and the girls stuck inside picture frames.^[14][15] The music video also references the 1980 film The Shining in a scene where members Irene and Yeri are dressed up as the Grady twins. Forbes called the music video "B-movie schlock retrofitted to K-pop perfectionism".^[16]

Internationally, RBB received generally positive reviews from critics. Natalie Morin of Refinery29 opined that while their last album Summer Magic was "an expression of their bright, fun "red" side, RBB highlights their soft, sultry "velvet" side". She added that the EP acted as "a sequel to their January mega-hit 'Bad Boy'". She also said the group "has a penchant for high drama, and the video for "RBB (Really Bad Boy)" plays right into it. Set in a retro "Hollywood" movie set — imagine being so powerful that you bring back Halloween on the cusp of winter".^[17] Caitlin Kelley of Forbes remarked that "As a whole, "RBB" is like if cocktail music became anthemic pop and then soundtracked a horror movie. The harmonies are complex, and vocal ad libs fill every nook and cranny of empty space". She also talked about the rest of the album and stated that "Red Velvet has a reputation for never skimping on their B-sides", asserting that "All of the songs on the six-track RBB EP are strong enough to stand on their own" and called "Sassy Me" the standout track from the album, saying it's a "self-empowerment anthem" that imbues the group's "flair for experimentalism".^[16] The album ranked fifth on Idolator's '10 Best K-Pop Albums Of 2018' list.^[18]

Upon its release, RBB quickly topped over seventeen countries' iTunes chart.^[19] Comparing to the group's previous release Summer Magic, the extended play was less commercially success in their native country. With only a tracking day due to the album being released on Friday instead, the extended play debuted and peaked at number three on the Gaon Album Chart and finished as the eighth best-selling release on the November 2018 issue of the Gaon Monthly Album Chart, having sold over 84,092 copies.^[20][21] By this, the EP was the group's tenth consecutive top-three entry, but their lowest peak to date on the chart. It eventually placed 49th on the 2018 year-end Gaon Album Chart, having sold a total of 94,367 copies.

The extended play, however, achieved bigger success for Red Velvet in the United States, topping both the Billboard Top Heatseekers Album chart and the World Digital Song Sales chart for the first time with the release of "RBB (Really Bad Boy)". According to Nielsen Music's report, RBB sold a total of 5,000 equivalent album units in the week ending December 6, with 3,000 in album sales, earning the group their best sales week in the States. It also charted at number two on the Billboard World Albums Chart, becoming their third top-two entry on the chart.^[22] Elsewhere, the album debuted at number fifty-one on the Billboard Japan Hot Albums chart, number ninety-two on the French Download Albums chart, and number sixty on the UK Album Downloads Chart, becoming the group's second entry in the United Kingdom following the release of Summer Magic.^[23][24][25]