If you subscribe to the Pokémon Bank service, a 3DS app that allows you to send your Pokémon from Pokémon X, Pokémon Y, Pokémon Alpha Sapphire, and Pokémon Omega Ruby to the cloud for storage, you’ll be able to get three Pokémon.
You’ll get Regirock,
Each of them will be level 50 and will have a hidden ability. You can claim them by logging into the Pokémon Bank service and then go to the Pokémon Link option of any of the four above mentioned games. That is, of course, as long as you have a subscription to the service, which is $4.99 annually. You can capture them in Alpha Sapphire and Omega Ruby, but it certainly wouldn’t hurt to get a few more cool Pokémon, even if you already have them. If you haven’t subscribed yet, you still have plenty of time to redeem this offer as it’s valid through October 31st.
In case you weren’t aware, you can also log in to any of the four 3DS Pokémon games and claim Celebi.
To get your own Celebi, you just go to the startup menu of any of the four games, select Mystery Gift, and someone will appear in a Pokémon Center and give it to you when you speak to them. You’ll need a free slot in your current party to collect Celebi. Celebi will be available through March 24th, so you better get on this quickly.