Successfully complete training mode on all five difficulty settings to receive all items in original mode.
Bonus options in Boss Mode
Successfully defeat and obtain a ranking for all bosses in "Boss Mode" to unlock a "Emperor" and "Fight All Bosses" options.
Bonus room
Successfully complete the game without any hostages being killed.
Get shotgun or grenade launcher
On the first chapter before you fight judgement, there will be a bridge and two zombies. Jump down and there will also be a door under the bridge. Shoot it and a old woman steps out and gives you either a shotgun or a grenade launcher.
Infinite continues
Successfully complete training and boss mode. Then the "Continue" option will change to "Free Play".
Napalm gun
Kill the first three zombies in level 1 with perfect head shots. If done correctly, the napalm gun will appear on the gorund.
Score display
At the main menu, press Left(2), Right(3), Left, Right, Start on a standard controller or light gun D-pad. If you entered the code correctly, a "0" score will appear at the top left portion of the screen.