How do we unlock the Eidolon legendary skinset for Allies?

There's a combined arms mission called "the challenge" that is apparently linked to it. In order to unlock the challenge you need to be at the menus and hit down and hold it for a second, then down three times, then down and hold for another second.

(In an order like this  -_ _ _-)

That should play the battlefield theme and unlock the challenge.

It is now confirmed, that you unlock the Eidolon Skinset after finishing the challenge map. This seems to be one of the hardest easter eggs to complete. Looking at the youtube video, it took them more than two and a half hours. :D

THE ENDING OF THE BABEL STAIRCASE EASTER EGG - Battlefield V (unlock eidolon skin) 

need 4 players and over 2 hours, that a bit long I know it challenge to get an Easter eggs, Already have hard time to play with my friends, I try to connect with people on Xbox that want to do this challenge and spend 2 hour or more to get this... I thinking I pass this one, I did enjoy the one in BF1 and get that awesome Peacekeeper 

Appreciate the replies.

Cbf doing this though just for a skin, and I've uninstalled this game now to make room for Cyberpunk 2077.

RIP BFV.

Lmao! Thinking that dumpster fire game is better then this dumpster fire game. 😢

@ElliotLH @IEchoa The link works perfectly fine. If you are talking about the assingment itself, that one does not show up automatically. You have to enter a morsecode in the main menu of the game to activate it first. Use the space bar on PC (X / Triangle on console) and press the key in this manner: long, short, short, short, long.