hearthstone's upcoming DLC features a unique five "wing" system spread out into content. The first wing is planned to be free for the duration of the release event with each subsequent wing costing $6.99 or the equivalent 700 in-game gold.
What's unique about this upcoming DLC is the wing system actually stems from its popular MMORPG partner World of Warcraft wherein a raid on a boss named Naxxramas actually exists. The wing system is symbolic of each of the five wings on Naxxramas in World of Warcraft.
"We’re skimming the slime pools, stitching together our finest Abominations, and preparing the Necropolis for an Adventure you’ll never forget—Curse of Naxxramas is coming, and we know you’re just dying to get in and play!"
Unlike the majority of hearthstone, this DLC is actually aimed towards the single-player side of hearthstone. Each wing the DLC features will contain 2-4 bosses for the player to defeat with each wing guaranteeing at least 1 legendary card. In addition, all players who have beat the bosses in both regular and Heroic mode will receive a new cardback to use during their gameplay.
In addition to the regular cards, players can unlock up to a total of 30 different cards from the new DLC. 15 of these have been reported to come from the separate bosses, 1 for each wing completed, and 9 for the class challenges. The way to obtain the 30th card is currently unknown, but it is speculated that obtaining all 29 cards will unlock the 30th.
To check out what else will be featured in the upcoming DLC you can view the future updates at us.battle.net