https://www.gamespot.com/articles/fortnites-ghost-portal-back-bling-is-easier-to-get/1100-6462498/

As part of a recent update Fortnite developer Epic Games introduced Halloween-themed cosmetics to unlock. The coolest among them is the Ghost Portal Back Bling, which emits ghostly apparitions when equipped. However, players complained that unlocking it was too difficult and, in response, Epic has made it easier for a limited time.

As detailed on the Fortnite subreddit and on Twitter, from October 12 at 10 AM ET / 3 PM BST / 7 AM PT until October 14 at 11:59 PM ET / 4:59 PM BST / 8:59 PT, simply playing 20 matches is enough to get the cosmetic. You don't have to win, as merely taking part in 20 matches is enough, and next week the challenges attached to the Back Bling will auto-complete and the item will unlock.