After completing the game, there will be a post-credits sequence where you chase General Hemlock around the city and you must destroy his zombie-harvesting droids. As soon as the cutscene finishes, starting the min-battle with the General's helicopter plane thing, hop off the roof and grab a few assault rifles from the nearby gun shop if you don't already have some on you. You will have a follower for this round, however they will work more on keeping zombies off of you while you follow the red triangle on the map (the aircraft) and destroy the droid things that come out of it to pick up the King Zombies. Ignore the King Zombies entirely to ensure a lot of droids come out of the ship, and they ignore you anyway so know worries there. The ship will move from Ingleton, to Central City, to Almuda and finally to Sunset Hills, with two locations in each district excluding Almuda, which has only one.
Once you've destroyed the 60th droid, a cutscene will appear and the final boss battle will begin. For the fight against the General, your best bet is to stay on the platform with him, in medium range, so he isn't constantly kick/punching you or shooting grenades at you. Guns are the best bet for this as a result, and there are a couple scattered around the area. If you run out of ammo, resorting to a couple quick attacks before rolling out of combat will work as well.