Billie Eilish kicked off Halloween weekend on a high note.

On Friday night, the Grammy-winning singer took the stage at Los Angeles’ Banc of California Stadium, where she starred in the live concert presentation of The Nightmare Before Christmas. Eilish took on the role of humanoid rag doll Sally, the shy but caring love interest of protagonist Jack Skellington.

“Peeing my pants,” the 19-year-old chart-topper wrote ahead of Friday’s concert. “I’m so excited.”

Eilish first treated the audience to a performance of “Sally’s Song,” originally sung by Catherine O’Hara and written by famed composer Danny Elfman, the four-time Oscar-nominee who also voiced the character of Jack.

“And now it is my great pleasure to announce a very special guest star, singing the part of Sally—please give a warm, not bad, welcome to Miss Billie Eilish,” Elfman told the crowd.

Fan videos of the concert show Eilish donning a Sally-inspired getup, complete with a patchwork dress and body paint that resembled stitching. Shortly after performing “Sally’s Song,” the singer returned to the stage to sing “Simply Meant to Be” alongside Elfman.

Other peformers included Weird Al Yankovic as Lock and Ken Page in his original role as Oogie Boogie.

The Nightmare Before Christmas concert will return to the Banc of California Stadium on Halloween night. The event comes three months after Eilish released her sophomore studio album, Happier Than Ever.