Along with the Witchwood expansion, tomorrow kicks off the Year of the Raven, rotating the cards available for play in standard formats. It also brings in a new Druid hero, updates to the game’s daily quests, and a number of new card backs that you can earn for various challenges. So you still have to wait just a little bit longer to really get in on the card-slinging fun, but at least you won’t have to wait for a patch tomorrow.
Hearthstone expansion approaches very quickly. It’s arriving tomorrow, as a point of fact. Of course, the patch for the 135-card expansion is taking place today, so you’ll be all patched and ready when the cards are actually usable. This also means that you should make sure to do any pre-purchasing today rather than tomorrow, since the associated pre-purchase goodies fade away at midnight.
Source: Official Site