The first wing, the Arachnid Wing, is open to all for free from now until around September with additional wings being opened by paying. You can obviously pay with real world money or save up gold in-game and pay for it that way. There are some really cool cards in this new set and they all work off the use of Deathrattle (when it dies the effect triggers).
Will you be heading back into the world of Hearthstone to find out what treasures await you?
Let me know!