Make sure you can spend an hour or so killing this monster alone. It is better to have Defender or Martyr because they are faster. When you first appear, kill all the zombies that are near you. Explore the street, picking up the machine gun and killing zombies on the way. Follow the fence all the way up to the opening. Be careful as there are many zombies and a few gargoyles. Once you have killed most of the zombies, go into the school area. Stay away from the gate so you do not activate the Boss too early. Explore a little bit, killing all of the zombies, getting health, and picking up the machine gun in the little playground near the exit. After you are sure everyone is dead, follow the fence (on the inside) until the intermission is activated and you have to kill the Boss. There are two ways to kill him: running around the fence shooting him while he is stuck; or the complicated but more reliable way as follows. Once the Boss is following you, go into the school yard and up to the tree. Stay next to the fence and wait until he is near. Jump over any ground attacks and kill the skitters. Once he is near the tree, quickly run away and go on to the other side of the fence (you should be on the street). Shoot him with everything you have, minding the skitters. It will take awhile but you will not use any lives.