POYONG
"A new event has begun around the globe. This event gives the Mega Stones for Mega Gardevoir, Gallade and Lopunny, as well as the Mega Stone, Diancite. This means all Mega Stones are now available to players. This is given with the code: POYONG. Like before, there currently is no end date known for this distribution so be sure to get it while you still can."
Code: POYONG
Source: serebii.net