Differences from MK3
Pop up combo added
Bike Kick now drains the run bar so he cannot rush in for a combo after connecting it mid-screen
Move List
Basic Moves
Liu Kang is the only character in the game to use his rear fist first to punch, subsequently, this has no affect on his juggling ability. His jabs in general are pretty normal. His sweep has normal range, but a bit of recovery to it. His uppercut is pretty good, but his HK hits noticably lower than some. His JP and JK are very high, similar to Kung Lao's in MKII and has an easy time beating out others because his forward and back jumps are a bit higher than everyone else's. His ducking LK is not as good as say Sonya's, or Kung Lao's, but it gets the job done, as well as his ducking LP for run jab escape. The straight up JK is a little short on range. His roundhouse is amazing. It has ridiculous range and is almost impossible to not connect it. Use it often, and use it well. It is possible to juggle a Dragon Kick off it if you happen to hit it close enough.
Special Moves
Dragon Kick
F, F, HK
14% Damage
The Dragon Kick is a fast, horizontal air attack with some strange properties. If you are too close to an opponent, the Dragon kick will go over them and land instantly on the other side, this might actually be something you will want to use because it will create some temporary confusion but as long as you know what the situation is you can take the upperhand. If the Dragon Kick is blocked, Liu Kang will land, and then go into a double animation where he is vulnerable to ground combos for an instant, timed to coincide with the recovery of the other character. You basically want to use it to extend combos, and occasionally as a wake up or a sudden attack. Like any move, it becomes easily scoutable with overuse.
Bike Kick
Charge LK for 3 seconds, release LK
12% Damage
The Bike Kick is used similarly to the Dragon Kick, except it can possibly lead to further damage in the corner, and occasionally you can combo a standing LK off it mid screen if you get it out right on time. If you get it in the corner and are overlapping your opponent when you land, it is easily possible to get his 7 hit combo off it with a sweep for 47%. From there you can run jab and mix up. The Bike Kick is a very good wake up attack because its collision starts up quickly. Do not over abuse this or people will bait it, and Liu Kang will go into punishment mode when it is blocked. You can use it to extend corner combos as well.
Fireball
High: F, F, HP (Can be done in-air)
Low: F, F, LP
13%
The Low, High Fireballs and Air Fireballs still have some use, but limited to generally full screen tactics and zoning. You can throw out a low or high fireball after his 7 hit combo to keep them pinned down, and air fireballs are good as well for pinning down, but try and keep them very low. Air Fireballs can also be used to extend corner combos, by doing JKs as early and high as possible, then doing the Air Fireball as low as possible, enabling you to rejump and repeat a few times. Unfortunately since all his attacks are double damage protected after the pop up, his corner combo damage is very low for the effort it takes to do them.
Finisher Moves
Fatality 1
F, F, D, D, LK (Next to)
Kang disappears, then he sets the victim on fire. Then he comes back to visibility.
Fatality 2
U, D, U, U + BL + RUN (Anywhere) (Hold Block)
Kang disappears, then drops a Mortal Kombat Machine on him/her, then he reappears.
Friendship
D, D, D, RUN (No Block in Winning Round) (Past Sweep)
Kang makes a shadow puppet of the MK dragon on a movie screen that comes down.
Animality
D, D, U (Mercy First) (Sweep)
Kang turns into a dragon and Bites the top Half of the body off. Just like his MK2 Fatality.
Babality
D, D, D, HK (No Block in Winning Round) (Past Sweep)
Mercy
Hold RUN, Wait 1 Second, D, D, Release RUN (Round 3) (Past Sweep)
Stage Fatal
RUN, BL, BL, LK (Next to)
Strategy
As Liu Kang
Liu Kang is a another one of those lower end of the mid tier characters, ranked in the neighborhood of 17th, who can be a pain in the right hands. He has a number of options to play around with, wake up bike kicks, dragon kicks, air fireballs, High/Low Fireball mix ups and the roundhouse of God. Mix up run jabs with his 4 hit kick combo, and when midscreen always do his 7 hit combo rather than his pop up when it is available for free, or off a jump punch starter. The 7 hit with a jump punch does 39%, and his pop up combo to JK, air fireball, dragon kick does 32%, not worth the effort. In the corner it is possible to link a sweep, standing LK or HK after his 7 hitter, and sometimes it is a good idea to throw a low fireball out after the 7 hitter, and mix that up with a high one once in a while to keep them guessing. The only time you will want to use his pop up combo is in the corner to set up multiple airfireball juggles, as it is relatively easily to compensate for the lost damage, but not by much. He has a very nice punisher that requires a bit of timing, aaHPHP, JK, air fireball, dragon kick in this case, without the double damage protection of his pop up combo, does 56%. It is a very useful tool to counter Human Smoke and Ermac's damage if you catch a blocked teleport, make sure you take a running step before you do the HPs, and cancel the second HP with the run button to allow yourself more time to get the JK high in the air. Abuse his roundhouse as much as you can, and try to link dragon kicks off it mid screen for some psychological advantages, as it is very easy to know when you will connect a Liu Kang roundhouse. Everynow and then throw out a wake up bike kick from close range, similar to Kano's cannonball.
VS Liu Kang
Combos
Liu Kang has a hard time relaunching characters because of the height and arch of his jump, but it is still possible to relaunch combo Jax, The Robots, Sheeva, Kung Lao, Nightwolf, Sub-zero, Kabal and Shang Tsung, but it is hardly worth the effort as the added damage for just one relaunch is about 13%. 
Basic Juggles: 
1. jump punch starter, HP, HP, B LP, aaHP, JK, airfireball 7 hits 28% 
2. aaHP,HP, JK, air fireball or Dragon Kick 4 hits 42% 
3. Bike Corner (in corner), HP, HP, BL, LK, LK, HK, LK, sweep, standing LK, or standing HK depending on opponent 9 hits 47-48% 
Advanced Juggles: 
1. aa(HP,HP), JK, air fireball, dragon kick 5 hits 56% (BP) 
2. jump punch starter, HP, HP, B LP, late JK, airfireball, dragon kick 7 hits 32%
3. jump punch starter, HP, HP, B LP, deep JK, aaHP, JK, air fireball 8 hits 32% 
4. (close to corner as a punisher) aaHP, JK, air fireball, RH, Dragon Kick 5 hits 66% 
5. (close to corner as a punisher) aaHP, JK, air fireball, aaHP, high fireball, standing HK 6 hits 69% 
6. (Half screen from corner as a punisher) aaHP,HP, 3X JK air fireball (over 100%, and you can leave off the 3rd JK air fireball and replace it with roundhouse, dragon kick if you don't have them high enough off the juggle)
7. (Near corner), jump punch starter, HP, HP, B LP, JK, air fireball 3X, aaHP, fireball, standing LK doable on just about every, but very difficult in concept, 13 hits 50% (you can also finish it with RH, run in HK, or RH dragon kick also for 50%)