From Bulbapedia, the community-driven Pokémon encyclopedia.
This is a reverse-chronological list of game-based Pokémon distributions that were given away using a game-based method to all region Pokémon games in Generation VI.
List of game-based Pokémon
Special Demo Version Mega Pokémon
The following two Pokémon are caught by the player (as "Orlando") during the first scenario in Pokémon Omega Ruby and Alpha Sapphire's Special Demo Version. Steelix is available to players using the Japanese region version of the Demo and Glalie is available to players using the American region, PAL region, or Korean region version of the Demo. The player can talk to Steven after the adventure to set up a transfer to the player's full Omega Ruby or Alpha Sapphire game via Pokémon Link, and will be able to pick it up once the game is out.
Pokémon Bank Celebi
This Celebi was available to players who accessed Pokémon Bank from December 25, 2013 to September 30, 2014. This Celebi has three IVs of 31 for three random stats. It could be transferred to Pokémon X and Y using Pokémon Link.