Including the single-player adventures!
older card packs are no longer available for sale. Since the mode began last year, players have been forced to craft content from two expansions and three single-player adventures if they wanted "Wild cards" to their collection. Thankfully, this is about to change - Blizzard will soon be selling Wild card content for a limited time.
Once active, Hearthstone will once again allow packs to be purchased for the Goblin vs. Gnomes and Grand Tournament expansions. What's more, you'll be able to pick-up classic story-based adventures - Curse of Naxxramas, Blackrock Mountain, and League of Explorers.
While these cards still won't benefit you in Standard Play, there are some wonderful combos to be work with here. It's also a great chance to experience any locked adventure content - the fantastic cheesy dialogue from Curse of Naxxramas is well worth a playthrough.
The Wild cards are presumably being put on sale to celebrate the Hearthstone Wild Open, which started today. All Wild content will be made available "in the coming weeks" for a limited time.