Everything Fal1phor said was right. BUT i ve also found another solution to do it yourself!!!!!! on the last stage, "Final Showdown" here are the steps:
1. When it starts, QUICKLY go left to the enemy then push down, x,x then x,x,y,y,y, do it ocassionally till they start sparking then input the command that appears over thier head. Whenever a zombie is close to you, DO NOT HESTITATE! push B and slam them, it also works for temporary invicibility.
2. when the guy starts charging you on his horse, do what Fal1phor said.
3. when the guys is off the horse, ignore all enemies and start warping up, up,up again and again and again. HERES THE KICKER! the guy (boss) will kill those 2 annoying assasins for you, when they re dead, then land, grab zombies and when the boss teleports above you, dont hestitate to shoot at him but! Keep a real close eyes on those zombies, they ll swat you, which is extremely annoying!
4: Whens its over... Kick back and pop a beer (or a soda if you re underage) and enjoy the pop up of [ 15 pts Master Of Arcade Dishwashing] achievment on your tv!