When you have to fight the big zombie in the graveyard, kill the purple zombies first. Then, run round the graveyard and collect the mushrooms if needed. If the big zombie is firing at you, go close to him so that he starts following you. Do a sword attack then start running around the graveyard again. The mushrooms reappear. Get them if needed. Keep doing a sword attack on the zombie until he is defeated. Do not attack the zombie in armor that is near the big zombie's side; when you kill it, the purple zombies come back again and you will have to kill them all over again. If the big zombie starts to fire at you again, then go close to him and he should draw his sword and follow you.