Hearthpwn

5:27 PM EST: We've updated our Arena Simulator to now display the GvG cards. Go practice some drafts!
4:22 PM EST: Added a video of the new gameboard in action.
4:16 PM EST: It looks like you can get some of the new cards in constructed if they can be randomly summoned from the card pool, like through Webspinner.
3:40 PM EST: iPad Hearthstone patch will be available once Apple verifies the patch. (Source)
3:28 PM EST: Arenas continue to reward you with Classic packs. GvG packs will be rewarded once the expansion launches. (Source)
3:20 PM EST: To get the free arena run, you must login between December 4th and the 8th to get the credit.
3:08 PM EST: PATCH IS LIVE! Restart your Battle.net client to get it!
2:57 PM EST: Zeriyah tweets "We're still working on the patch"
2:20 PM EST: Breaking News status for NA has been updated saying cards have changed.

Goblins vs Gnomes Invades the Arena

Patch is now LIVE! Restart your Battle.net client to get the update!

To get the free arena run, you must login between December 4th and the 8th to receive your credit. The credit can be used whenever you start your next run.

Quote from Blizzard

Hearthstone Patch Notes – 2.0.0.7234 – Goblins vs Gnomes Invades the Arena!

Thanks to a bit of meddlesome tinkering—and perhaps a little goblin-induced sabotage—all Goblins vs Gnomes cards are now available to choose from in the Arena!

You heard that right—those pesky pint-sized engineers (being an impatient bunch) have jury-rigged the Arena to give Hearthstone players a sneak peek at what’s in store when Goblins vs Gnomes officially launches next week. In doing so, they’ve calibrated things to throw all Goblins vs Gnomes cards into the Arena deck-building mix ahead of schedule. Speaking of peeking, Spectator Mode will also be online, so you’ll also be able to tune your transmitters in to watch your friends play!

Goblins vs Gnomes packs will be available to purchase via the in-game Shop upon the official release of Goblins vs Gnomes on December 8^th!

Goblins vs Gnomes

• Don’t let Goblins and Gnomes have all the fun building things: All Goblins vs Gnomes cards have been added to the Arena and can be chosen even if you do not have them in your Hearthstone collection.
• All Goblins vs Gnomes cards can be found easily in My Collection using the search function, and all Goblins vs Gnomes cards have a “gear” watermark in the card text box.
• Expert card packs have been renamed to “Classic” card packs. Classic card packs are still available to acquire in the in-game Shop as well as through Crafting Mode.
• New minion type “Mech” has been added. Use Mechs along with other Mechs for surprising (often devastating) results!
• An all-new interactive Goblins vs Gnomes-themed game board has been added. Turn the gears, wind the springs, and try not to blow anything up in the process. We warned you.

General

• Spectator Mode has been added. Watch your friends play through their games of Hearthstone and observe their epic victories all with the click of a button! Spectator Mode is accessed through the Friends list by clicking on the “Spectate Match” button next to your friend’s name.

Card Changes

• Flare now costs 2 mana, up from 1.
  • Flare allowed the Hunter an advantage versus decks that revolve around Secrets, while also allowing the Hunter to draw a card for little cost. We want to encourage a variety of decks in Hearthstone. With this change, Flare will continue to be useful against Secrets decks, but will be weaker against other decks.
• Gadgetzan Auctioneer now costs 6 mana, up from 5.
  • Gadgetzan Auctioneer’s ability allows for a player to potentially draw many cards for little cost. Card draw and card advantage are important to the game – overall, games are less interesting when a player draws their entire deck. This change brings Gadgetzan Auctioneer’s cost more in line with its power level.
• Soulfire now costs 1 mana, up from 0.
  • Soulfire, along with fast and powerful minions, allowed Warlock rush decks to get ahead on the board and stay ahead. We’ve upped Soulfire’s mana cost by 1 to slow down the Warlock rush deck just a bit and allow more players time to react and interact against the Warlock.

Bug Fixes

• The left-most enemy minion can once again be targeted on a full board if Counterspell counters a Secret.
• Nozdormu, self proclaimed “Master of Time”, once again gives players 15 seconds a round instead of 30.
• Blood Imps will no longer target Imp Masters with no life left. It’s dead, Jim.
• Baron Rivendare in the Naxxramas Adventure has fixed his heater and will no longer cast Frostbolt on himself.
• Faceless Manipulators will now copy the Echoing Ooze as well as its effect.
• Faceless Manipulators will now copy the Echoing Ooze as well as its effect.
• Faceless Manipulator now functions properly when targeting minions with Enrage that refuse to follow the rules. 
• Druid of the Claw is embracing his wild side and now becomes a Beast minion type upon switching Cat Form or Bear Form.
• Multiple mechanical minions have been upgraded to Mechs, unlocking additional synergy with other Goblins vs Gnome cards: Harvest Golem, Damaged Golem, Alarm-o-Bot, Demolisher, Mechanical Dragonling, and all of Gelbin Mekkatorque’s AWESOME inventions.
• Kel'Thuzad's mastery of undeath has been tempered and it will no longer resurrect itself after perishing at the hands of Ragnaros the Firelord.
• Gnomes have been hard at work fixing Goblin “upgrades”, forcing our engineers to step in and fix the fixes that the gnomes “fixed”.  Ultimately, a number of display issues and other bugs have been resolved.

Goblins vs Gnomes in the Arena!

Your next arena is free, as long as you start it during December 4th to 8th.

Quote from Blizzard

Thanks to a bit of meddlesome tinkering—and perhaps a little goblin-induced sabotage—all Goblins vs Gnomes cards are now available to choose from in the Arena!

You heard that right—those pesky pint-sized engineers (being an impatient bunch) have jury-rigged the Arena to give Hearthstone players a sneak peek at what’s in store when Goblins vs Gnomes officially launches next week. In doing so, they’ve calibrated things to throw all Goblins vs Gnomes cards into the Arena deck-building mix ahead of schedule. Speaking of peeking, Spectator Mode will also be online, so you’ll also be able to tune your transmitters in to watch your friends play—check out the It’s Better With Friends section of our BlizzCon Fireside Chat blog for more on how it works.

Another unexpected side-effect of this mechanical meddling: anyone who logs in to the game between December 4 and December 8 automatically gets their next new Arena run for free! It’s a zero-risk chance to see some of the new cards in action—with a high-risk chance of something going explosively awry. And if you’re already in the middle of an epic Arena run that won’t be finished before December 8, don’t worry—just make sure to log in during the pre-launch period, and you’ll be good to go.

Once the expansion officially launches starting on December 8, you’ll be able to permanently add Goblins vs Gnomes cards to your collection by purchasing packs, using dust, or earning Arena rewards—until then, it’s a great time to hop into the Arena and tinker with all the new Mechs and other devices that’ll be available for players to collect. New strategies and card choices await, so dive in today!

New Gameboard Preview

We've uploaded a Youtube video of the new gameboard in action. Some really cool interactions!

New Cards Summoned in Constructed

Trikoot found a nice surprise when his Webspinner died; It summoned Gahz'rilla! This happened in constructed.

Undocumented Changes

Quote from HearthPwn

• Arena button now lights up with a blue border when you have an active arena run.
• Some heroes have new voiceovers when they're selected in the arena.
• Cards which scale based on conditions (like Kill Command) have a Yellow border when their condition is met, like Combo cards.
• Archmage Antonidas says "Ahha" when he creates a Fireball

Goblins vs Gnomes Cards

Our card database now has all of the Goblins vs Gnomes cards and they're also available for use in our deckbuilder. Go make your awesome Goblins vs Gnomes deck and share it over on our forums. 

All the cards can be found on our dedicated Goblins vs Gnomes info page, or can be viewed in our card database.