Zombies are deceased humans reanimated by Element 115 and are the primary antagonists of the game mode of the same name. Their only method of attacking is melee but only two successive attacks from the zombies are required for the player to go down without Juggernog.
Hell Hounds were first introduced on beta 1.1, whenever they spawn the demonic announcer will say "FETCH ME THEIR SOULS", At the end of a dog round the player recieves a Max Ammo. Currently the hellhounds are unstable on the PSP version and will make the game freeze. Unless of course you use a custom firmware and speed up memory stick access speed and the in game cpu speed to the highest possible speed. This will not only make the game run smoother, but will also let you reach higher levels.