http://bulbanews.bulbagarden.net/wiki/Hidden_Ability_fully-evolved_Unova_starter_Pok%C3%A9mon_distribution_announced_for_American,_PAL_region
"The fully-evolved Unova starter Pokémon with their Hidden Abilities will be available to American and PAL region Pokémon Omega Ruby and Alpha Sapphire using universal serial codes. Serperior is already available for American and PAL region games.
All three Pokémon will be available until Nov. 30, 2015. Serperior became available today using the special password POKEMON497, as revealed on Pokémon.com, the same as the Japanese distribution. Emboar will be available starting Jan. 29, 2015, with its special password to be revealed on Pokémon.com. Samurott will be available starting Feb. 5, 2015, with its special password to be revealed in a Pokémon Trainer Club newsletter.
[...]Its gender and Nature are random, and it has no held item.[...] These Pokémon can be obtaining using the "Get with code" option in Mystery Gift. This option can only be used on games updated to v1.2."