As you guys saw the GX world has been introduced to dueling links with two new structure decks and GX characters to unlock and play with. Mokuba was also introduced to the game in a BINGO event.

To unlock the new legendary duelists you need to perform various tasks like reaching higher stage level on GX or for example for Aster summon 200 dark monsters.

Check out http://duellinks.gamea.co/c/z28ibd98#cp459529 for more details on unlocking.