The code can be redeemed until March 29, so best not to sit on this for too long. Each game that was registered to PGL can get one code apiece.If you signed up to the PGL with USUM before January 30th, the Master Ball code is now out. Once you're logged in, follow this link:-
https://3ds.pokemon-gl.com/present/b9a1c64a-696c-4c8c-8c0a-8ef148ba190a