Battlefield 1/Blood Moon
On the map Zeebruggee in the Turning Tides expansion pack, a blood moon appears if 4 players are all wearing different Horsemen of the Apocalypse dog tags. The moon starts to turn red and the Horsemen of the Apocalypse are heard galloping once the 4th player has joined the game. All players on the server will see and hear the blood moon event. The moon stays red for the remainder of the round.
It is possible to trigger the blood moon with just 2 people. 1 player has to join a server with 1 of the Horsemen tags equipped and stay there as to not restart the server. Another player then joins with a different Horsemen dog tag equipped. The server will remember the tags, so the 2nd player can keep leaving and joining with a different Horsemen dogtag until the 4th dogtag triggers the blood moon.