As people who play Hearthstone will know, the game has just launched on Android tablets. It is also available through the Amazon app store, who are running a promotion that refunds half the cost of card packs and arena entries in Amazon coins.
The promotion states that the offer is only on the 15 and 40 bundles, but for the past few days I have been using my £5 bespoke voucher to purchase multiple sets of 2 packs for 199 Amazon coins, and getting 100 coins refunded each time. As I had over 100 coins in my balance already, it worked out that I received 20 packs for a fiver.
Even if you buy the coins for the going rate, you will still be getting the packs at almost half price.
If you don't have an Android tablet, you can always do what I did, and install DuOS (download here - http://www.amiduos.com/).
This emulator comes with Amazon appstore preloaded.
To log into the my account on the app, I had to remove the authenticator from my account, as the login screen just kept looping when I entered my credentials.
The promo material states this is a limited offer, but it doesn't have an end date listed. So get those GvG packs while they are available cheaply!