Banks first announced the possibility of a mixtape on May 10, when she tweeted, "So y'all will be getting, 1991 EP this month, the FANTASTIC mixtape for the summer, and Broke With Expensive Taste, in the Fall". On May 30, Banks took to Twitter again to announce her plans to alter the title of the mixtape from Fantastic to Fantasea. Banks released the album cover of "Fantasea" via Instagram on July 9. Banks later confirmed that Fantasea would have 18 tracks (15 originals and 3 remixes). Via Twitter, Banks spoke on the mixtape saying "Fantasea is almost kind of a first album of sorts....but it happened by mistake.... It's weird". "This is a test run... I tried a lot of cool things... Sounds I thought were progressive, beats made by close friends, different flowsss."
In 2015, upon the launch of music streaming service Tidal, Fantasea, along with other various artists mixtapes, was uploaded to the service under the record label of Winter Records.
Fantasea was subject to highly positive reviews from music critics. The Guardian 's Graeme Virtue wrote that the mixtape "showcase[s] an artist brimming with ideas" and gave it a rating of four stars (out of five).Spin gave the album a rating of 8 out of 10 and wrote that the album "makes her [Banks] sounds mega-industrious."
On May 11, 2012, Banks released the track "Jumanji" online as a free digital download. Produced by Hudson Mohawke and Nick Hook, the track served as the first song set to feature on the upcoming mixtape. A second track, "Aquababe"—produced by EPROM and Machinedrum—was released online on June 13. Ahead of its release on July 11, Banks released a third track, "Nathan" on June 30. Featuring American rapper Styles P, "Nathan" was produced by Drums of Death. Azealia spoke on the song Nathan saying "I'm that rap girl who's out here and doesn't have another rapper behind her, but she's got all this mouth and she's all over the place, So [this collaboration] was cool for me [because I'm like] 'What ya'll gonna say now, when I bust out with that Styles P record?' Ya'll not gon' call me fake and make fun of me for having one song. Yeah, I make lil' dance music and ya'll got jokes, whatever—watch when I come out with the Styles P record." Banks released the song "Neptune" featuring Shystie online on July 10, 2012. She also released music videos for "Luxury" and "Atlantis" on September 27 and November 11, 2012, respectively.