Basic Moves:

Moves that require only a button press:

HIGH PUNCH - Produces a punch to the face. Many can be strung together in succession by rapidly pressing  the  button.       
LOW PUNCH - Your character will punch the opponent's midriff. Many can be strung together in succession by rapidly pressing the button. Not as powerful as a high punch but can hit the opponent while they are ducking.
HIGH KICK - Smacks your opponent in the face with a powerful kick
LOW KICK - Not as powerful as the high kick but a little faster to recover, kicks the opponent in the abs.
BLOCK - Blocks attacks            
RUN - Lets your character runs forwards for a limited amount of time. This is great for attacking opponents who are running away from you. Pay attention to the run meter (the smaller meter underneath your health bar) - this will indiciate how long you can run for.
SIDESTEP INSIDE - This takes advantage of Mortal Komabt 4's 3D battle arenas, and is useful for dodging projectile attacks or disorienting your opponent slightly before attacks. This steps TOWARDS the screen. On the arcade, this was accomplish by pressing Down, RUN, RUN. However on most of the home system conversions, Sidestepping is assigned it's own button.
SIDESTEP OUTSIDE - Exactly the same as sidestepping inside except you sidestep AWAY from the screen. On the arcade, this was accomplished by pressing RUN, RUN. As with the other sidestep move, most of the home systems had a button dedicated to sidestepping.
    
Combination Moves:

Moves that require a button to be pressed simultaneously with a direction:  

Jump Kick - Jump + either KICK button.    
Jump Punch - Jump + either PUNCH  button.         
Pressing up plus kick or punch will result in your character punching  or kicking in midair without moving in a direction. If jumping  towards or  away from the opponent, pressing punch or kick will cause your  characrter  to extend their limb a little further to hit the opponent and  will cause more damage. A Jump Kick is more powerful than a Jump Punch, but  Jump Pucnhes are better for winning aerial battles.      
Uppercut - Down + HIGH PUNCH.
The Uppercut has lost a lot of it's firepower in the fourth installment...it is nowhere near as powerful as it is in the 2D Mortal Kombats. It still serves a purpose though.
Sweep - Back + LOW KICK      
Sweeping knocks your opponent onto their back by tripping them over.   
Roundhouse - Back + HIGH KICK
Your character spins around and gives your opponent a heavy kick to the side of the head, causing them to spin through the air.
Weak Kick - Down + LOW KICK
Not really useful unless your opponent is ducking and avoiding your other attacks...weak and slow.
Throw - Forward + LOW PUNCH
Must be standing right next to your opponent. Different characters throw in different ways, but all throws do good damage. Throws cannot be blocked normally.
Bone Breaker - Forward + LOW KICK
Perhaps your character's most potent move, the Bone Breakers are a painful addition to Mortal Kombat 4. Executed in similar fashion to a throw (you need to be up close to your opponent), they deliver damaging hits to your opponent. Different characters have different Bone Breakers, each with varying damage. Some leave your opponent open to be hit again. Like a throw, they cannot be blocked normally.
Block Throw/Bone Breaker - BLOCK + diagonally down + away
Pressing down and away while blocking will prevent your opponent from executing a throw or a bone breaker.
Power Hit - Forward + HIGH PUNCH       
Some characters elbow, some headbutt, but the basic premise is the same - a strong hit to the opponent in close quarters. Most characters can perform a two-hit combo by pressing HIGH PUNCH twice.
Attack with weapon - Forward OR Back OR Down + HIGH PUNCH or LOW PUNCH
Your character must be holding a weapon to be able to execute these moves, and what your character does depends on what weapon your character is currently holding. Experiment, especcially if you pick up a weapon that isn't your own.

Special Notes:

Mortal Kombat 4 is a major facelift to the series, the game is now in Full 3D (although the gameplay is still essentially the same as a 2D with the exception of sidesteps).

New features have been added, most notably the Bone Breakers and the Weapon system.

With the Weapon system, each character has their own specific weapon, which requires a direction and button combination similar to a special move to "pull" the weapon out. Once your character is in possesion of a weapon, you can use it to attack your opponent in different ways. What kind of attack depends on the weapon.

You can knock weapons out of your opponent's hands by hitting them. You can then pick up your opponent's weapon and use the attacks of that weapon. The same applies to you and your weapon, of course.

You can throw whatever weapon you are holding at your opponent by simply executing the direction and button combination to pull your own weapon out.

Several battle arenas have objects that can be picked up and thrown at your opponent. When they connect, they are very damaging. They can be large boulders and even skulls.

To pick up a weapon or a throwable object, stand over it and press Down+RUN at the same time. Weapons will be picked up and held in your hands. Throwable objects will be thrown immediately.

Stage Fatalities can only be performed on certain stages. The character's "Fan Fatality" is performed on The Prison while the "Spike Fatality" is performed on Goro's Lair.

Each character now only has two distinct Fatalities (as well as the stage fatalities). That means, no animalities, brutalities, friendships, babalities or whatever.

Each character has their own Unique combos, and for the sake of space (and the fact that I could miss a few) I will not list them here. Experiment to work them out...Mortal Kombat 4 has a slightly different combo system to MK3, UMK3 and MK Trilogy, and they are slightly easier to pull off, so try different punch and kick combinations (and sometimes block) and you'll soon be pounding the pulp out of your opponents!

Character Weapons:

Below is a list of the different weapons available in the game for the different characters:

Kai - Machete Knife
Raiden - Stone Mallet
Shinnok - Nagimaki (wooden stick with a blade on the end)
Liu Kang - Flamberge Sword
Reptile - Battle Axe
Scorpion - Broad Sword
Jax - Spiked Club
Reiko - Spiked Club (guess they ran out of ideas)
Johnny Cage - Smooth-Edged Scimitar
Jarek - Jagged-Edged Scimitar
Tanya - Boomerang
Fujin - Crossbow
Sub-Zero - Ice Sceptre
Quan Chi - Spiked Mace
Sonya - Windblade

Special Moves:

JOHNNY CAGE

Weapon: Forward, Down, Forward, Low Kick
High Fireball: Down, Forward, High Punch
Low Fireball: Down, Back, Low Punch
Shadow Uppercut: Back, Down, Back, High Punch
Shadow Kick: Back, Forward, Low Kick
Nut Crack: Block + Low Punch (does not work on Tanya or Sonya)

Fatality 1 : Forward, Back, Down, Down, High Kick ( Close )
Fatality 2 : Down, Down, Forward, Down, Block ( Close )
Fan Fatality: Down, Down, Forward, Forward, High Kick
Spike Fatality: Back, Forward, Forward, Low Kick

LIU KANG

Weapon: Back, Forward, Low Kick
High Fireball: Forward, Forward, High Punch
Low Fireball: Forward, Forward, Low Punch
Flying Kick: Forward, Forward, High Kick
Bicycle Kick: Hold Low Kick for 3 seconds, release

Fatality 1 : Forward, Forward, Forward, Down, Low Kick + High Kick + Block ( Sweep Range )
Fatality 2 : Forward, Down, Down, Up, High Punch ( Close )
Fan Fatality: Forward, Forward, Back, Low Punch
Spike Fatality: Forward, Forward, Back, High Kick

FUJIN

Weapon: Back, Back, Low Punch
Whirlwind Spin: Forward, Down, Low Punch
Dive Kick : Down + Low Kick while in Mid air
Levitate Cyclone: Forward, Down, Forward, High Punch
Slam : Back, Forward, Down, Low Kick ( Opponent must be in levitate cyclone )
Flying Knee: Down, Forward, High Kick

Fatality 1 : Run + Block, Run + Block, Run + Block, Run + Block ( Sweep Range)
Fatality 2 : Down, Forward, Forward, Up, Block ( Half Screen )
Fan Fatality: Down, Down, Down, High Kick
Spike Fatality: Back, Forward, Back, High Punch

REPTILE

Weapon: Back, Back, Low Kick
Acid Spit: Down, Forward, High Punch
Super Jab: Back, Forward, Low Punch
Invisibility: High Kick + Block
Crawl Attack: Back, Forward, Low Kick

Fatality 1 : Hold High Punch + High Kick + Low Kick + Low Punch and press Up ( Close )
Fatality 2 : Up, Down, Down, Down, High Punch ( Half Screen )
Fan Fatality: Down, Forward, Forward, Low Punch
Spike Fatality: Down, Down, Forward, High Kick

TANYA

Weapon: Forward, Forward, High Kick
Pink Fireball: Down, Forward, High Punch
Air Fireball: Down, Back, Low Punch in Mid air
Split Kick: Forward, Down, Back, Low Kick
Corkscrew Kick: Forward, Forward, Low Kick

Fatality 1 : Down, Down, Up, Down, High Punch + Block ( Close )
Fatality 2 : Down, Forward, Down, Forward, High Kick ( Close )
Fan Fatality: Back, Forward, Down, High Punch
Spike Fatality: Forward, Forward, Forward, Low Punch

SCORPION

Weapon: Forward, Forward, High Kick
Spear: Back, Back, Low Punch
Teleport Punch: Down, Back, High Punch
Air Throw : Block in air
Fire Breath: Down, Forward, Low Punch

Fatality 1 : Back, Forward, Forward, Back, Block ( Sweep Range )
Fatality 2 : Back, Forward, Down, Up, High Punch ( Close )
Fan Fatality: Forward, Forward, Down, Down, Low Kick
Spike Fatality: Back, Forward, Forward, Low Kick

RAYDEN

Weapon: Forward, Back, High Punch
Lightning Bolt: Down, Back, Low Punch
Teleport: Down, Up Flying
Torpedo Launch: Forward, Forward, Low Kick

Fatality 1 ( Close ): Hold Block ( Forward, Back, Up, Up, High Kick )
Fatality 2 ( Close ): Down, Up, Up, Up, High Punch
Fan Fatality: Down, Forward, Back, Block
Spike Fatality: Forward, Forward, Down, Low Punch

KAI

Weapon: Down, Back, Low Punch
Falling Fireball: Back, Back, High Punch
Rising Fireball: Forward, Forward, Low Punch
Flying Fist: Down, Forward, High Punch
Super Roundhouse: Down, Forward, Low Kick
Handstand: Block + Low Kick ( Low Punch to Spin, Low Kick/High Kick to Kick and Block to Stand Up) 

Fatality 1 : Hold Block, Up, Forward, Up, Back, High Kick, release Block  ( close )
Fatality 2 : Up, Up, Up, Back, Block ( Half Screen )
Fan Fatality: Forward, Forward, Down, Block
Spike Fatality: Back, Forward, Down, High Kick

JAX

Weapon: Down, Forward, High Punch
Fireball: Down, Forward, Low Punch
Ground Pound: Forward, Forward, Down, Low Kick
Dash Punch: Down, Back, Low Punch
Back Breaker : Block in air
Multi Throw:
1st Throw: Forward + Low Punch
2nd Throw: Run + Block + High Kick
3rd Throw: High Punch + Low Punch + Low Kick
4th Throw: High Punch + Block + Low Kick
5th Throw: High Punch + Low Punch + High Kick + Low Kick 

Fatality 1 : Hold Low Kick 5 sec ( Forward, Forward, Down, Forward ) release Low Kick ( Close )
Fatality 2 : Back, Forward, Forward, Down, Block ( Close )
Fan Fatality: Forward, Forward, Back, Low Kick
Spike Fatality: Forward, Forward, Back, High Punch

QUAN CHI

Weapon: Down, Back, High Kick 
Weapon Steal: Forward, Back, High Punch (while opponent is holding weapon)
Air Throw : Block in air
Teleport Stomp: Forward, Down, Low Kick
Flaming Skull: Forward, Forward, Low Punch
Slide Kick: Forward, Forward, High Kick

Fatality 1 : Hold Low Kick, Forward, Down, Forward, release Low Kick ( close )
Fatality 2 : Up, Up, Down, Down, Low Punch ( half screen ) - copies opponent's 2nd fatality
Fan Fatality: Forward, Forward, Down, High Punch
Spike Fatality: Forward, Forward, Back, Low Kick

REIKO

Weapon: Down, Back, High Punch
Teleport: Down, Up Push Block to Slam
Turn-Around Spin: Back, Forward, Low Kick
Flip Kick: Back, Down, Forward, High Kick
Shurikens: Down, Forward, Low Punch

Fatality 1 : Forward, Down, Forward, Low Punch + High Kick + Low Kick + Block ( Close )
Fatality 2 : Back, Back, Down, Down, High Kick ( Half Screen )
Fan Fatality: Down, Down, Back, Low Punch
Spike Fatality: Forward, Forward, Down, Low Kick

SUB-ZERO

Weapon: Down, Forward, High Kick 
Ice Blast: Down, Forward, Low Punch
Ice Clone: Down, Back, Low Punch
Slide: Low Punch + Block + Low Kick

Fatality 1 : Forward, Back, Forward, Down, High Punch + Block + Run ( Close )
Fatality 2 : Back, Back, Down, Back + High Punch ( Half Screen )
Fan Fatality: Down, Up, Up, Up, High Kick
Spike Fatality: Down, Down, Down, Low Kick

JAREK

Weapon: Forward, Forward, High Punch
Ninja Star: Down, Back, Low Punch
Cannonball Roll: Back, Forward, Low Kick
Vertical Cannonball Roll: Forward, Down, Forward, High Punch
Ground Shaker: Back, Down, B+HK

Fatality 1 : Forward, Back, Forward, Forward, Low Kick ( Close )
Fatality 2 : Up, Up, Forward, Forward, Block ( Half Screen )
Fan Fatality: Forward, Down, Forward, High Kick
Spike Fatality: Back, Forward, Forward, Low Punch

SONYA

Weapon: Forward, Forward, Low Kick
Force Wave: Down, Forward, Low Punch
Air Throw : Block in air
Leg Grab: Down + Low Punch + Block
Teleport Punch: Forward, Back, High Punch
Bicycle Kick: Back, Back, Down, High Kick 
Flip Kick: Back, Down, Forward, Low Kick

Fatality 1 : Down, Down, Down, Up, Run ( Sweep Range )
Fatality 2 : Up, Down, Down, Up, High Kick ( Half Screen )
Fan Fatality: Forward, Forward, Down, High Punch
Spike Fatality: Down, Down, Back, Back, High Kick

SHINNOK

Weapon: Back, Forward, Low Punch
Fujin Impersonation: Forward, Forward, Back, High Kick
Jarek Impersonation: Back, Back, Back, Low Kick
Jax Impersonation: Forward, Down, Forward, High Kick
Johnny Cage Impersonation: Down, Down, High Punch
Kai Impersonation: Forward, Forward, Forward, Low Kick
Liu Kang Impersonation: Back, Back, Forward, High Kick
Quan Chi Impersonation: Forward, Back, Forward, Low Kick
Rayden Impersonation: Down, Forward, Forward, High Punch
Reiko Impersonation: Back, Back, Back, Block
Reptile Impersonation: Back, Back, Forward, Block
Scorpion Impersonation: Forward, Back, Low Punch
Sonya Impersonation: Forward, Down, Forward, High Punch
Sub Zero Impersonation: Down, Back, Low Punch
Tanya Impersonation: Back, Forward, Down, Block

Fatality 1 : Down, Back, Forward, Down, Run ( Close )
Fatality 2 : Down, Up, Up, Down, Block ( Close )
Fan Fatality: Down, Down, Forward, High Kick
Spike Fatality: Down, Forward, Back, High Punch

Secrets:

Kombat Kodes:

See the MK3 FAQ for explanations on Kombat Kodes.

111-111 - "Free Weapon" One weapon in the center at the beginning of the match.
100-100 - "Throwing Disabled" No throws or bone-breakers.
444-444 - "Armed and Dangerous" Start off with your weapons drawn.
666-666 - "Silent Kombat" No background music.
050-050 - "Explosive Kombat" Last hit causes loser to explode.
222-222 - "Random Weapons" Start with another weapon at random.
123-123 - "No Power ??" Start off with just a bit of energy above "DANGER" level.
555-555 - "Many Weapons" Weapons drop all over the stage.
060-060 - "No Rain" No rain on the Wind World stage.
002-002 - "Weapon Kombat" Both players never drop their weapons.
012-012 - "Noob Saibot Mode" Play as Noob Saibot.
020-020 - "Red Rain" Causes it to rain blood at the "Wind World" stage.
010-010 - "Maximum Damage Disabled" No Maximum Damage.
110-110 - "Throwing and Max Damage Disabled" No Throws and Max Damage.
011-011 - "Kombat Zone: Goro's Lair" Play at "Goro's Lair" Stage.
022-022 - "Kombat Zone: The Well" Play at "The Well" Stage.
033-033 - "Kombat Zone: Elder Gods" Play at "The Elder Gods" Stage.
044-044 - "Kombat Zone: The Tomb" Play at "The Tomb" Stage.
055-055 - "Kombat Zone: Wind World" Play at "Wind World" Stage.
066-066 - "Kombat Zone: Reptile's Lair" Play at "Reptile's Lair" Stage.
101-101 - "Kombat Zone: Shaolin Temple" Play at "Shaolin Temple" Stage.
202-202 - "Kombat Zone: Living Forest" Play at "Living Forest" Stage.
303-303 - "Kombat Zone: The Prison" Play at "The Prison" Stage.
001-001 - "Unlimited Run" Get an unlimited Run meter.
313-313 - "Kombat Zone: Ice Pit" Play at "Ice Pit" Stage.
321-321 - "Big Head Mode" The characters have over-sized heads

Other Secrets:

Fight as Goro

Successfully complete the game with Shinnok. Enter the character selection screen, choose the HIDDEN icon using Run, keep holding it, then press Up, Up, Up , Left to highlight Shinnok's icon, and press Block while still holding Run.

Fight as Meat

Enter the Group Mode Game and successfully complete the game with all sixteen characters. After this has been accomplished, select any character and begin a match. Your character will playing as Meat with all the moves of the character that was selected, but no skin!

Fight as Noob Saibot

Successfully complete the game with Reiko. Enter the 012 012 Kombat code in versus mode. Exit this match and enter the character selection screen, choose the HIDDEN icon using Run, keep holding it, then press Up, Up, Left to highlight Reiko's icon, and press Block while still holding Run.