The code to play Galaga with 2 ships:
During power up, press and hold keys (UP, L1, Triangle, Cross) on the 
player 2 controller.

This is the death from above move in which Law climbs up the opponent and 
falls on him. It seems to do about a 1/3 health bar damage to the opponent. You 
need to be close up and then hit LP + RP. (Left Punch and Right Punch at the 
same time) If you are not close enough to the oppponent Law will just put up 
his knee.

There are unblockable moves for some characters:
LAW: down/away left + right punches 
YOSHIMITSU: 
1) away, away + left + right punches 
2) away/down + left and right punches 
MICHELLE: away, away, away left punch NINA: down/away two punches 

Play in slow motion:
Anytime during the match just open the cd thing and even the slow motion 
replay will be slower, but while the Vs. screen appears you have to close it.

100% damage with Jack. (From the left side) Rotate the pad from back 
counter-clockwise to up-forward and push l-punch+r-punch for 16% 
damage. Rotate from back all the way around (counter clockwise) 5 
times and end up on up/forward then hit l-p+r-p for 100% hit. (Jack will count 
to five. Every complete circle is one count. When he says five hit lp+rp.)

When using armor king, do his suplex move and tap down, down, down 
and then hit both punch buttons before he starts falling backward, and he 
will change it into a super piledriver.

To get Devil Kazuya start the Galaga game and clear the first level within 
18.5 secs. You will then receive another ship. After receiving the other ship 
continue on through all eight levels. You have to clear all of them and you are 
only allowed one continue. After beating all eight levels the game will start. 
Go to arcade mode and select Kazuya using the start button not the punch or 
kick buttons. You will then have Devil Kazuya. 

An unlimited combo for Kazuya and Heihachi is:
s, s, c, c, c, s, s, c, c, c, s, s, etc... It is pretty hard to get started, but 
once you get it started, it's easy. If you mess up just hit x or t.