Story related, cannot be missed. Right after defeating the Sentinel Mark you will go head to head with Fred Dukes. Tips on defeating Fred Dukes: Fred is huge and that is his main weapon, he will pound on the ground with his hands and feet, using all his weight to knock you out of balance. Stay clear when he is going to attack and then move in to do damage. After doing some damage he will come running towards you and slide over the floor of the grocery store. Once he comes to a halt grab onto him with
, or if you are far of, lunge towards him with
. When on his back, you can 'steer' Dukes in the right direction by pressing
, doing so also depletes his health. Crash him into on of the four destructable walls in the middle of the grocery store for maximum damage. When taking on Fred Dukes also get the "Clean Up on all Aisles" achievement.