Hold L + Z + C-Up + C-Down at the title screen for approximately five seconds. The sound of a bang will confirm correct code entry and the character selection screen will appear. An entry for the "Car Park" level will be displayed at the top center of the screen. Press C-Left or C-Right to select a new starting level. Note: This also enables invincibility to most attacks. Explosions and special moves will still cause damage. Also, bazookas get 30 rounds of ammunitions and flare guns get 10 rounds. Alternately, hold R + Z + C-Up + C-Down at the title screen for approximately five seconds.
Select Mace as your character. When there are three opponents next to you, start running. When the enemy is in front of you, press B to do a double kick. It should kill the enemy. Also, if there three enemies touching you, hold Z and press A to get out of it and damage them. However, this hurts you, and if you do not have enough health you cannot do it (try running out of it).
Keep hitting the soda machines. Drink the cans that appear from them to restore a small amount of health.
The following objects can also be used as weapons.
Totally destroy a car, then Smasher can pick up the engine and use it as a weapon.
Destroy the airplane at the Airbase to use its gun.
Destroy the two large black structures found in the Hovercraft level to get a flare gun.
Destroy the police car in the Car Park level to get a rocket launcher.
Go to your left as soon as you enter the reception level and destroy the farthest box to get a pistol and 2 grenades.
After entering the Bronx level, keep going straight and pass the train that throws bombs at your character. Then, turn left and break open the brown gate to get a pistol in each of the two left boxes in the gate.
Destroy the first car on the bridge level to get a pistol. Destroy the second car at the end to get a shotgun.
Destroy the parked black car inside the gate in the Car Park level to get a shotgun.