Allow me to tell you the easiest ways to get this achievement.
First off if you are rich and or lazy you can buy 10 keys and unlock all cards in the decks...... Bam achievement.... I DON'T SUGGEST DOING THIS!!
Now in order to unlock all decks you should beat the campiagn, again i suggest using the green deck PACK INSTINCT.
Use a free key to unlock all green cards if you can.
Now with all decks unlocked and a campaign beat go to the campaign screen and choose an encounter called ..... CULT OF FLAME ... It is the second encounter of the campaign.
This encounter is very easy to beat.... They only play one card over and over.. Plus it cost 3 lands to play, they play second to you aswell so this all means you have 4 turns with only a 1/1 card to go up against..... CAN YOU SAY EASY?
So go through and play each deck by playing CULT OF FLAME over and over until you unlock 1 card for each deck and the achievement is yours!
Any questions or problems please post a comment!
Thanks!