Alien character  -  Enter “INVITE VISITOR” as a password. 
All standard characters  -  Enter “GANGS ALL HERE” as a password. 
Avalanche at the Ski Resort  -  Shoot down any three trees on one side and an avalanche will occur. This works well when people are by the trees. 
Big wheels  -  Enter “MONSTER WHEELS” as a password. 
Bonus characters and levels  -  Enter “WMNNWLHTSCUCLH” as a password. 
Change the Soundtrack  -  If you'd like to listen to something different, replace the Vigilante 8 CD with your favorite music CD after you've started a level. 
Cheat mode  -  Enter “GIMMIE DA WORKS” as a password to enable:

All standard characters 
Alien character 
Sand Factor and Secret Base levels 

Expert mode  -  Enter “HARDEST OF ALL” as a password. 
Homing missile power-up  -  Enter “DEADLY MISSILE” as a password. 
Identical vehicles (2P mode)  -  Enter “SAME CHARACTER” as a password. 
Invincibility  -  Enter “I WILL NOT DIE” as a password. 
Launch missile at Area 51  -  Start a game on the Area 51 level. Go through the gate (past the lasers) to the building. Drive "through" one side of the building. When you come out the other side, drive around the square and go under the two lights (one should already be green from driving through the building). Driving under the lights will turn the 2nd light green and the missile will launch at the enemy you have targeted 
Lunar gravity  -  Enter “REDUCE GRAVITY” as a password. 
Machine Gun Trick  -  If you have an autofire joystick you can increase the damage done with the machine gun. Set R2 to autofire when the button is pressed. This will enable a steady stream of bullets without overheating the gun. Your enemies don't have a chance! 
No enemies  -  Enter “GO SIGHTSEEING” as a password. Then select Arcade mode game. 

Passwords  -  Here are codes for every person's Quest Mode, passing it with "Objective Met": 
VIGILANTES:

Chassey Blue:
AOGIKYFGQQTWGA (Mission 1)
YMBEJEOPDHYHZV (Mission 2)
RIPJNYEPGFPJAI (Mission 3)
HGFTDDNMUBXRLV (Mission 4)

Slick Clyde:
TNLCROHSQAZDMQ (Mission 1)
QDANNFHMSLBMWF (Mission 2)
FYLYRFKEAHGGAW (Mission 3)
OIRYEEBGDBNHBJ (Mission 4)

Shiela:
EDAOHLJIOUEDBA (Mission 1)
HSDNTZSGVOGCLP (Mission 2)
NTWZYUQSPXMHMB (Mission 3)
BXINCWNWGCQVJF (Mission 4)

John Torque:
WSLZFBNQDTFDBF (Mission 1)
BXNJRYSXTYACKE (Mission 2)
IBXGFDQBSNISJQ (Mission 3)
ZCTEAFJVMNDJUT (Mission 4)

Dave:
PYQXPDUMJNBOUP (Mission 1)
OULIUZTJHPKWTD (Mission 2)
QYDJBUYBZTEUQC (Mission 3)

Convoy:
AIHJZNIFPZNFWA (Mission 1)
UKXCXCOAIGOKVH (Mission 2)
KHREIWYIZREYHK (Mission 3)
VSNKJVURSUNRWX (Mission 4)

COYOTES:

Loki:
THLOHJWURONKLQ (Mission 1)
VIBWYIVGOPAUWX (Mission 2)
CEJMULWPCYYAVS (Mission 3)
PGGOVIUNUQEIVU (Mission 4)

Houston 3:
BDPTGXUBXOCCKE (Mission 1)
GCTPCXCCIWXVUJ (Mission 2)
NXJFNPZXRAAGMB (Mission 3)
DTQQSKTRYIHGEN (Mission 4)

Boogie:
FOJGCRHLWMUQZV (Mission 1)
DRFIQVOUYIHGEN (Mission 2)
WCHPZDGBCYEDBF (Mission 3)
JHAZRUUMTLUYBG (Mission 4)

Beezwax:
YUYFNKTAQGLNYW (Mission 1)
TXXKKGEWRONKLQ (Mission 2)
KHUSNNWJXORZHK (Mission 3)
UIBRJCCYSARVH (Mission 4)

Molo:
EDDNXIAPNTRDBA (Mission 1)
ITAHZJRMYTLSJQ (Mission 2)
NPRJUYRYRAAGMB (Mission 3)
AKFQPUISMWAHWA (Mission 4)

Sid Burn:
LPHPMMDNMPEMVB (Mission 1)
PEONQGUNUQEIVU (Mission 2)
XOKIXDXBKQRFOJ (Mission 3)
OYROHGBDNLSJSI (Mission 4)

Playing Tip  -  Choose to be the UFO on the secret base level. Go into the top secret area (the place where all the lasers shoot you.) Start at one end of the big building and drive straight through. If you shoot above the missile launcher a missile comes out and shoots your targeted opponent. You can do this as many times as you want at either end. 

Roadkill Mines  -  To activate this attack press Left, Right, Down, MachineGun. This costs only two mines.
Note: This mine is invisible until you or an opponent gets close enough. These mines hold you for about 10-15 seconds before detonating. You can get away only if you are driving at top speed in one of the three fastest cars. 

Sand Factory and Secret Base levels  -  Enter “SECRET LOCALES” as a password. 

Secret Cars  -  On the OPTIONS screen, move the cursor to CONTROLLER SELECT then quickly press Up, Up, Down, Down, Left, Left, Right, Right, X, X, Square, Square, Circle, Circle, Triangle, Triangle. 

Ski Lift, Blimp and Bomber secrets  -  On the ski level go to the bottom of the hill and enter the lodge doors, your car will get onto the lift and it will take you to the top of the mountain. This works the other way as well.

In the Las Vegas level you can find the blimp flying over, watch where it lands then enter the door that opens. It will take off and allow you to fly it over the city, get over a building and wait until it drops you on the roof.

In the airplane graveyard you can drive your car between the flight tower and electric polls. The flight towers are located at each corner of the level, they are the towers with the flag on the roof. This will cause the B-52 bombers to come out and bomb your opponents.

In the farm level you can shoot the valves beside the water canal, then a huge wave will go through the canal damaging any car trapped in the canal.

In the secret military level you can shoot the ladders beside the stealth bombers, then go over to where the satellite dishes are located and drive by the red and green lights to make the bombers hit your opponent.

On the hover dam level you can hit the switch in front of the dam by the water to make an electric burst of energy go through the water zapping your opponent.

In the Canyonland level, get in the middle of the circle of rocks. A gold beam will come down and teleport you elsewhere.

On the level Sand Factory at one of the load things that a truck would pull in to load sand in the back of it you can shoot at one of the poles with the machine gun only once. An elevator will lower and you can get on it. This is an easy way to get on the upper levels. Search around for the loader!

On the snow resort level shoot 3 large trees to cause an avalanche! Boulders will start to roll down the slopes! 

Slow motion  -  Enter “SLOW MOTION ON” as a password. 

Special Attack Tip  -  Having a problem entering special attacks with the analog controller? There is an easy way to solve this problem. Go to options. Go to controller one (or whichever controller you are using). Set the digital pad "up" button to "Accelerate" and set the "down" button to "brake". Now you can steer with the analog and enter most of the special attacks with the digital pad! 

Special weapons 

Bruiser Cannon (Cow Puncher)
Cost: 2 shells
Press Down, Up, Down. Then shoot the machine gun to knock opponent’s vehicle backward. 

Bruiser Cannon (Scatter Blast)
Cost: 6 shells
Press Down, Up (x2). Then shoot the machine gun to discharge 6 cannon shells simultaneously.

Bulls’s Eye Rockets (Stampede)
Cost: 1 – 5 rockets
Press Up, Down, Up. Then the shoot machine gun to discharge up to five unguided missiles.

Interceptor Missiles (Halo Decay)
Cost: 2 missiles
Press Up (x2), Down. Then the shoot machine gun to cause your opponent’s homing missiles (or special attacks) to lock on to your missiles instead of your vehicle.

Interceptor Missiles (Turbo)
Cost: 1 missile
Press Up (x3). Then shoot the machine gun to use your own missile to propel your vehicle.

Roadkill Mines (Cactus Patch)
Cost: 1 – 6 mines
Press Left, Right, Up. Then shoot the machine gun to deploy a mine cluster.

Roadkill Mines (Magnetic Mine)
Cost: 2 mines
Press Left, Right, Down. Then shoot the machine gun to deploy a mine that will attract the opponent’s vehicle.

Sky Hammer Mortar (Crater Maker)
Cost: 5 shells
Press Down (x2), Up. Then shoot the machine gun to drop a crater-making bomb.

Sky Hammer Mortar (Turtle Turnover)
Cost: 2 shells
Press Down (x3). Then shoot the machine gun to overturn your opponent’s vehicle.

Turbos  -  To activate this code press up-up-up-machine gun. Costs one homing missile. When you do this a homing missile will latch onto the side of your vehicle and you will travel at the same speed as the missile. 

View all FMV sequences  -  Enter “SEE ALL MOVIES” as a password. Push X on the “Game Status” screen character. 

Whirling Blades at Farm  -  When you go to the farm level, shoot at the big windmill towers. When they fall, the blades will pop off and chase the nearest car.