Pokemon Bank is running a special deal that runs from March 4th through to October 31st. By accessing the 3DS application you will receive your own copy of Hoen's legendary trio Regirock, Regice and Registeel, each of these Pokemon will also come with its hidden ability. Note that Pokemon Bank does require a yearly subscription fee of $4.99US.
Here is the promotion rundown from the Pokemon Company:
“You can get the Pokémon trio by selecting the Pokémon Link option from the menu screen of your Pokémon X, Pokémon Y, Pokémon Omega Ruby, or Pokémon Alpha Sapphire game. Once you’ve received the Pokémon in Pokémon Bank, select Pokémon Link and the three Pokémon will be sent to a Box in your game. The three Pokémon will be sent one at a time from Pokémon Bank. Note that you can receive these Pokémon only once per Pokémon Bank account, even if you have multiple copies of Pokémon X, Pokémon Y, Pokémon Omega Ruby, or Pokémon Alpha Sapphire.
Each of the three Pokémon that you receive has a Hidden Ability, a trait they do not possess when found in Pokémon Omega Ruby and Pokémon Alpha Sapphire. This is your first chance to get these Pokémon with their Hidden Abilities, so don’t miss this opportunity!”
In addition here is your rundown of the Regi's for your information:
With the Hidden Ability Sturdy, if Regirock has full HP and is hit with an attack that would normally knock it out, it will be able to endure the hit with 1 HP remaining. This is a great Ability for Regirock to have, being a Rock type with many weaknesses.
Regice’s Hidden Ability Ice Body allows it to restore HP when the weather condition is hail. Regice is strong against opponents that attack it with special moves. By using Hail, it can recover HP throughout the battle while doing even more damage!
Ability: Ice Body
Registeel’s Hidden Ability Light Metal reduces its weight by half. This decreases the damage it will take from moves such as Low Kick and Grass Knot that are more powerful the heavier the target is. It is especially good for Low Kick, a Fighting-type move that is super effective against the Steel-type Registeel. Roll with those supereffective punches and strike back!
Ability: Light Metal
Moves: Iron Head