There was no shortage of celebrities onstage last weekend at the first installment of this year’s Coachella Valley Music and Arts Festival in Southern California, where Doja Cat, Billie Eilish and even Will Smith performed.

Ms. Eilish surprised spectators by joining Lana del Rey for the folk-rock singer’s first Coachella set since 2014. Mr. Smith, who started his career as a rapper, also shocked many in the audience by performing a rendition of his song “Men in Black” with dancers dressed as aliens during the reggaeton singer J Balvin’s set.

But some of the highest-profile performers at the festival weren’t there to work: Rihanna and ASAP Rocky, along with Taylor Swift and Travis Kelce, came as spectators, even if neither couple could exactly blend in with the crowd.

At Coachella — an orgy of brand activations, parties and musical performances — celebrities are but one reliable component. Another is fashion, which typically tends toward the ostentatious. That was mostly the case last weekend, during which these 15 looks stood out — some for being opulent, others for being over-the-top and a couple for being surprisingly simple.

Doja Cat: Most Harebrained!

Of the many outfits worn by the singer and rapper during her set, this get-up involving few clothes and strategically arranged extensions might have stolen the show — if only by a hair.