Duos is a game mode in Fortnite: Battle Royale. The game typically takes place with fifty teams of two. However, it may turn out to be less, due to players wishing to do solo-duos. When playing, it takes place similar to solos. The objective is to survive until the end and be the last player/team alive. When fighting, it differs from solos because when the player reaches zero health the player gets "knocked".
Being knocked means that the player can move by crawling, and can't deal damage to opponents. When the player is knocked, they constantly lose health and can take extra damage from other players, the storm, or falling damage. A knocked player can either be revived by their teammate, or they will die. When they are revived they are able to do everything the same as if they never got knocked, but they will return with 30 health. If a player gets knocked from fall damage and they have shield, when revived they will have 30 health and the shield that they had before the fall. The same applies if knocked down in the storm. If the player dies when knocked, they will spectate their teammate or the player that knocked them.
To do a solo-duo, the player must click no-fill. They will have no teammate, and they will have to face other duos.