The fastest achievement (with all due respect due to white shadows) is not to do thorns castle over and over again. Play time attack select Forgotten Forest and then just simply let the time run out. Each game takes 1 minute 30 seconds. So So So easy, got all mine in the space of a couple of hours (got two x-boxes and two copies of kameo.) but even if you dont have that it should only take both boosters 3-4 hours tops... Enjoy!