Dark Albion is unlocked once you have completed the credits level of the main game. Dark Millfields is the first level of this second playthrough.
Simply take your time and be careful. Best tactic is to use a ranged character such as Reaver or Ben Finn. The giant hollow man in the second bandit arena can be a pain, but dodge away from him and you should be fine.
As CourseOfAction suggests in the comments, you can enter the bandit arena to trigger the enemies and then retreat. Then shoot the enemies from off screen with your ranged character, until the game says "GO."
As Spilner notes, if you select the farm at the path select section, you can get hit in the chicken dodging mini game and still get the achievement.
Note you can definitely still got the achievement after pressing RT to use your special attack.