Question: destiny 2 how to unlock mysterious box?
Answer: Speak with Ada-1. Visit Ada-1 to receive the Black Armory Key Mold, the final key needed to unlock the Mysterious Box. ... 
Go to the Leviathan. ... 
Complete the Bergusia forge. ... 
Return to Ada-1. ... 
Complete a Rare Black Armory bounty. ... 
Complete the Shattered Throne. ... 
Complete the Pyramidion Strike.