From VG247: “The v8.51 update is now available for Fortnite, so lets see what changes are coming in the last week of Season 8.
The Shadow Bomb item has been added to Battle Royale. Engulf yourself in darkness with this new item where youll be invisible to enemies, have your speed increased and can double jump.”
Source: N4G PC Fortnite v8.51 updates adds Shadow Bombs, Diner prefabs and the Duet assault rifle