Players will be able to play Curse of Naxxramas without spending a dime.
Hearthstone's Curse of Naxxramas expansion will bring with it a host of new, singleplayer boss encounters, and of course, plenty of new cards. As Hearthstone is a free-to-play title, many were worried that this content would be behind a paygate that free customers can't get to. The good news is, you'll be able to experience the expansion in its entirety without spending a dime, as players can use the game's in-game "free" currency - gold - to unlock all of the additional content.
Not dissimilar to how the original World of Warcraft raid instance was, Naxxramas will open its gates one wing at a time, with a new wing opening each week. The wings of Naxxramas will open in the following order: Arachnid Quarter, Plague Quarter, Military Quarter, Construct Quarter, and Frostwyrm Lair.
As an added bonus, players who begin their adventures in Naxxramas during the launch event will gain free access to the first wing: the Arachnid Quarter. Blizzard stressed that the "launch event" will last a full month, so players should have plenty of time to take advantage of it.
After that, each additional wing will set you back 700 gold, or $6.99 USD. If you've got deep pockets and little patience, you can purchase all five wings in a bundle pack for $24.99.
Keep in mind that purchasing Curse of Naxxramas wings in bundles does not open or grant access to those wings faster than the one-wing-a-week schedule, but it does ensure that you'll be able to dive into the next challenges as soon as they unlock.
Additionally, Blizzard also revealed that just like in WoW, Hearthstone's Naxxramas will have a "heroic mode". Once you've beaten all of the bosses, you can battle them again in the heroic mode difficulty, which rewards victorious players with a new card back for their decks.