The outfit was added as part of a promotion by CipSoft. You can obtain it as a reward if one of your friends invited by you via Invite New Players feature buys something in the Store. If three of your invited friends buy a product in the Store, you will receive the First Addon, if ten of your invited friends buy a product in the Store, you will receive the Second Addon. The outfit and addons will be available to all characters on your account, you don't have to assign them to a specific character.
Upon earning the full outfit, players used to earn the achievement The More the Merrier. However, this achievement was removed from the game.
Full Walking Animations from the Reward Page: