To promote the new card set & content expansion named The Boomsday Project, Hearthstone is giving away a few valuable mystery gifts, including a Legendary minion and 6 free card packs from the latest expansion, available for you to grab for a limited time.

Six Card Packs Giveaway

For a limited time after launch, log in to claim a random Class Legendary minion (or Hero card) and three card packs from The Boomsday Project, FREE. Then, when The Puzzle Lab -a single-player game mode to be added with the The Boomsday Project expansion- opens on August 21, you may log in to obtain 3 more free The Boomsday Project card packs.

About The Boomsday Project

The Boomsday Project is Hearthstone’s latest expansion, featuring 135 all-new cards. This update also brings Arena updates, game mechanics updates, and a few card changes, as well as some bug fixes and feature improvements.
The Boomsday Project launches on a region-by-region basis, beginning with the Americas, Europe, and Asia, followed by China a short time later.

– Europe: August 7 at 19:00 CEST
– Americas: August 7 at 10:00 PDT
– Asia: August 8 at 02:00 KST (01:00 CST)
– China: August 8 at 06:00 CST

About The Puzzle Lab

The Puzzle Lab is a free-to-play single-player game mode to be added with the The Boomsday Project expansion when it becomes available on August 21, 2018. The Puzzle Lab is categorized into various puzzles that the player will have to solve:

– Board Clear: Clear the battlefield of all minions.
– Lethal: Destroy the enemy hero in a single turn.
– Mirror: Create a board state in which both sides are perfect mirrors of one another, including minion positioning, attributes, etc.
– Survival: Survive the enemy’s Hero Power.

Source: Link