A new Hearthstone update that allows players to get guaranteed Legendary cards is already in effect, according to the community.
According to a Blizzard Hearthstone update last month, if you open the first 10 packs in a set, you will get a guaranteed Legendary. This applies to players who have never opened a single pack from a set. Furthermore, if you open a Legendary in a card pack, it will be a Legendary card from the same set that you do not already own. If you own either the standard or gold version of a Legendary card, you won’t get a duplicate of it until you own all Legendary cards in that set.
A Reddit post from Tank1an has confirmed that this update is working. The “1 guaranteed Legendary per 10 packs once per expansion” rule works for Classic, Mean Streets Of Gadgetdzan, Whisper of the Old Gods, Grand Tournament, and Gnomes vs Goblins. Other users on the thread commented that they had collected their Legendaries as of three hours ago, though there is currently a bug right now that allows those that have already opened a pack in a set to get this benefit. There is no word from Blizzard whether this bug will be fixed though.
On a related note, Blizzard is also offering a Journey To Un’Goro promotion: if you buy any of the standard card pack bundles, you’ll get extra packs from it. Check out the chart below to see how much of a bonus you’ll get.