Gamedoctors is offering a last minute holiday gift for all of their fans. Before the App Store goes into lockdown tomorrow, where developers won’t be able to modify prices, descriptions, etc for their apps for the holiday stretch, ZombieSmash HD for iPad is being offered at a very kind 66% off, making it only $.99 for the next few hours.

ZombieSmash HD is a physics-based defense game, where you need to defend yourself against hordes of ravenous creatures of the undead. Housing a revamped campaign from the original iPhone and iPod touch version, the iPad native creation certainly provides plenty to enjoy.

Three amazing gameplay modes offer hours of challenging excitement and replayability:

• Campaign Mode challenges players to survive for 31 intense days against the mounting zombie threat.
• Endless Siege Mode confronts them with a never-ending zombie assault – hold out as long as possible, racking up an ever-rising body count.
• Sandbox Mode gives you all the tools to rain destruction down on those stinking, moaning zombies without any of the peril.

You’ll find yourself booming, blasting, and otherwise mangling zombies for endless addicting hours with high-resolution 3D graphics, ragdoll physics, an original soundtrack, Game Center leaderboards and achievements, and 25 zombie-butt-kicking weapons, specials and upgrades like landmines, sniper rifles and asteroids.

Take a look inside of the entire experience and find out why we consider ZombieSmash HD a “must buy” in our full review.

ZombieSmash HD is compatible with iPad running iOS 3.2 or later. Game Center features require iOS 4.2 or later. As a reminder, while the price is $.99 in the U.S. store as of this post, please be sure to double-check your local App Store price before clicking or tapping the Buy button.

Even though this great game is being offered at just a buck, Gamedoctors has been kind enough to offer AppAdvice readers a generous serving of 20 promo codes to win. Your only choice now is whether to splurge on the gracious $.99 price while it lasts or take your shot at getting a copy completely free.

To have a chance at winning one of eight ZombieSmash HD promo codes, simply hit that blue tweet button near the bottom of this page or retweet this post from your favorite Twitter app before 11:59 PM PST tonight (December 22nd). We will then search the Twitterverse for all of the retweets and randomly choose our lucky winners. The winners will be notified via Twitter, so please be sure to follow us so we can send you your promo code via a direct message.

Non-Twitter users and those of you who want to increase your odds of winning can simply leave a relevant comment below before 11:59 PM PST tonight to have a chance at winning one of the other twelve ZombieSmash HD promo codes.

Feel free to participate in the giveaway via either or both methods. Only one entry per person per method is allowed, totaling up to two entries per person if using both.