Guilty Gear X2 Cheats

Either

Defeat them in Survival mode, they appear at levels 210, 220 and 230.

or

Complete all endings in Story mode.

or

Complete 40 missions in mission mode.

Unlocking Justice, Robo Ky, and Kliff the lazy way.
Place your PS2 in training mode for 4 days (96 hours total)
*Note that the 96 hours includes the play time as well, so the requirement may be less than 96 hours depending on how much time you spent on this game (in game wise, not on the starting screen/menu).

To select a different stage, highlight a character and press R2.