A Very Potter Musical

Lord Voldemort Dolores Umbridge Quirinus Quirrell Ron Weasley

Irvin is a huge fan of Team StarKid, naturally because of their A Very Potter Musical trilogy. He makes a point of dressing up whenever he attends one of their concerts or shows, and a majority of those costumes (seen here) are from the AVPM shows.

Technically, Draco Malfoy also counts for this purpose, given Irvin wore it for a StarKid-adjacent event and met Lauren Lopez in it, but the costume is indistinguishable from the regular Draco costume (given Irvin's behavior as Draco skews toward the AVPM version anyway).