Hearthstone has introduced a new Recruit-a-Friend feature that can help get friends back (or into) the game. If you invite them, you can earn a free Shaman hero and some packs.
To get the goods, share your recruitment link (to get the link, you have to be logged into Battle.net). After using it, your friends will get a welcome message that gives them a free pack of cards once they create an account and play the intro missions. Once they do so, you’ll get your reward.
The first recruit will earn you Morgl the Oracle, the new hero, while the next four will get you a Classic card pack for each recruit. However, for the recruit to be eligible, they can’t have any classes already at level 20.