Life PreserverG 10

You win a white deck after beating the second campaign mission. You don't need to unlock any cards for it, the standard deck should work fine.

Go to Custom Duel, and hit X to open the advanced options. Bump your starting handsize up to 9, and the AI's down to 5. It can't hurt to turn the AI down to the lowest difficulty in options, either. Elspeth is a good opponent to use here as her deck is very defensive. If you don't see a lot of lifegain in your hand, don't be afraid to draw a new hand a few times, you won't be able to keep more than 7 in your hand after your first turn ends anyway.

Play very conservatively, leaving everything untapped to block to keep your opponent from attacking and focus on gaining life. Only use Pacifisms on creatues that you can't block and kill. One good combat trick is to block with Goldenglow Moth, then cast Holy Day. The moth won't die, and you'll still gain the 4 life.

This is also boostable in a player match with a friend.