Right now the first wing of Hearthstone's expansion Curse of Naxxramas is free to download. That won't always be the case, though. Today Blizzard revealed when this offer will expire.
"The Curse of Naxxramas launch event is ending soon!" Blizzard announced on the Hearthstone forum. "This means you have until September 30 at 11:59 p.m. PDT to log in to Hearthstone and unlock the Arachnid Quarter for free. If you haven’t experienced all of the creepy-crawly fun of The Arachnid Quarter, now is a great time to skitter into Curse of Naxxramas: A Hearthstone Adventure. Emerge from the wing victorious and you’ll earn new (web-covered) cards for your Hearthstone collection!"
Starting on October, the Arachnid Quarter will be the same price as the four others: $6.99 or 700 gold. You can also purchase several wings at the same time. Here are the prices for buying multiple wings:
After completing the Arachnid Quarter on Normal, you can revisit the fights with Class Challenges. You have to beat Grand Widow Faerlina as a Druid and Maexxna as a Druid while using set decks. Your rewards for these challenges will be a new card for each class.
The last challenge is to beat the bosses on Heroic mode. Each opponent has increased health and new abilities on Heroic. You'll need to have a very clear strategy and a well-suited deck to take them down. If you need help, check out our Curse of Naxxramas guide.
The point of all this is that Arachnid Quarter's worth grabbing while it's free. You may find the A.I. bosses an entertaining diversion - and even if you don't, you're getting some new cards. They could help you get an edge in Ranked Play. Nerubian Egg's turned out to be a very potent addition to some decks.
Curse Of Naxxramas was released over the course of several weeks this summer. The fifth and final wing, Frostwyrm Lair, arrived last week. They collectively offer 15 bosses, 9 class challenges and 30 cards to collect.
Naxxramas is the first of multiple single-player expansion packs for Hearthstone. The future expansion packs shouldn't take nearly as long to be released, though.
"We are currently laying a lot of the groundwork for Adventure Modes in general and intend to be able to leverage this groundwork for future Adventure Modes," Blizzard said in July. "This should definitely help with future Adventure Mode rollout times."