It was written by Alejandro, Farruko, Eric Duars, Franklin J. Martinez, Ricardo Lloyd Johnson, and Windel Edwards, while the production was handled by Urbani Mota and Luis J. Romero.

A Spanish language melodic reggaeton and dancehall song, it is about the singers living out all of their "fantasies" with the girl they are crushing on.

The track received positive reviews from music critics, who noted Alejandro's charisma and the song's "eminent success".

An accompanying music video, released simultaneously with the song, was filmed in Miami and directed by Gustavo "Gus" Camacho.

It experienced commercial success in Spanish-language markets, reaching number one in Peru, and the top 10 in several other countries, including Colombia and Venezuela.

The accompanying music video for "Fantasías (Remix)", released simultaneously with the song, was filmed in Miami and directed by Camacho.

[6] Musically, "Fantasías" is a Spanish language melodic reggaeton and dancehall song,[1][7][8] written by Alejandro, Farruko, Eric Duars, Franklin J. Martinez, Ricardo Lloyd Johnson, and Windel Edwards.

Its production was handled by Urbani Mota and Luis J. Romero,[9] and the track runs for a total of 3 minutes and 19 seconds.

"[1] The lyrics include, "Cómo le puedo hacer, pa' convencerte / A solas quiero tenerte / Qué tú harás si te digo, mil fantasías contigo" (How can I do it, to convince you / I only want to have you / What will you do if I tell you, a thousand fantasies with you).

In 2022, Ernesto Lechner from Rolling Stone ranked the track as Alejandro's 22nd-best song, saying it proved "that he had as much charisma — if not more — as any high-profile reggaetonero", while it "was one of the first collaborations where up-and-coming Rauw glittered under the spotlight".

[14] "Fantasías" was nominated for Best Song New Generation at the 2020 Premios Tu Música Urbano, but lost to "Otro Trago" by Sech and Darell.

It subsequently peaked at number four on the chart issue dated November 3, 2019, becoming Alejandro's first top five hit in the country and Farruko's second.

It reached number one in Uruguay,[32] and peaked in the top 10 of Argentina,[33] Bolivia,[34] Colombia,[35] Costa Rica,[36] Dominican Republic,[37] Ecuador,[38] El Salvador,[39] Honduras,[40] Latin America,[41] Mexico,[42] Nicaragua,[43] Panama,[44] Paraguay,[45] and Peru.

In her review for Billboard, Jessica Roiz described the remix as "fiery" and noted that "each artist brings their individual flow to the track", highlighting Natasha's "fierce vocals" and Alejandro's "impeccable dance moves".

[62] Bolivar Feijoo of Wow La Revista named it "a unique collaboration",[53] while Los 40 staff described it as "great".

It reached number one in Peru,[69] and peaked in the top 10 of Colombia,[70] Costa Rica,[71] Dominican Republic,[72] Ecuador,[73] El Salvador,[74] Guatemala,[75] Honduras,[76] Latin America,[77] Nicaragua,[78] Panama,[79] Paraguay,[80] Venezuela.

It depicts Alejandro, Anuel AA, Natasha, Farruko, and Lunay singing and "having a great time together at a beach party".