To end the 20th anniversary Mythical Pokemon event, Meloetta's WiFi distribution is live. Go grab her, and once you do have her in your party, take her to the cafe in Mauville City (man near the entrance) in ORAS, or a house in Snowbelle City (behind the Pokemon Center, on Abomasnow's right, talk to the male Ace Trainer) in XY to learn Relic Song, that allows Meloetta to change formes.
Also, for Genesect last month, if it is in your party, talk to a guy in Mauville City (Northeast staircase) in ORAS, or a Hiker in Ambrette Town (in the fossil research lab) in XY to receive Genesect's 4 Drives to change Techno Blast's type.
If you missed out on Arceus' GameStop event, a 2nd chance event is announced, used the shared code ARCEUS20 for US games, and ARCEUS2016 for Euro games. The event will last until 31st December 2016, so don't miss out on God again!