Arlecchino has been mentioned in multiple voice lines, and she finally made her first appearance during the "A Winter Night's Lazzo" trailer that also revealed all the remaining Harbingers.

Source: https://gamerant.com/genshin-impact-arlecchino-weapon-type/

Pierro, also known by the name "The Jester" is the Director of the Fatui and the first member of the Harbingers which is why he can be seen sitting at the top of the table during the trailer video.

Source: https://gamerant.com/genshin-impact-leak-harbingers-multiple-delusions/

Take on additional skill-based goals to unlock three unique variants of the Harbingers badge, and collect all three to unlock a grand final badge for completing everything.

Source: https://comicbook.com/gaming/news/apex-legends-harbingers-collection-event-patch-notes-ps5-xbox-pc/

The Harbingers Collection Event includes a total of 24 new cosmetics.

Source: https://comicbook.com/gaming/news/apex-legends-harbingers-collection-event-patch-notes-ps5-xbox-pc/