At the title screen press Down, Right, Right, Up, Start.
Every Characers Special:
Press Triangle + Square during a fight.
Guilty Gear Mode:
Play thru all of the Survival mode, Beat Everyone and you will get both all the costumes and the GGmode in the Options menu. I don't know what it does, but i found that if you have 2 kei's and ggmode on both, Kei is hunched over and his moves are 50% more damage!
Alternate Costumes:
To get other costumes press a button other than the X button. Such as Start will give you a yellow caracter, hold start and you can get a glowing one. REMEMBER! you must unlock all the costumes you must fight them in Survival.
Respect Move:
When you are 1v1 with a friend make him use Respect several times, but don't attack them during it. It brings up your Tension Bar!