Play as Devil Gundam
Beat story mode with all fighters, then use Master Gundam in 64 mode and defeat Devil Gundam. Devil Gundam will now be accessible.

Play as Judecca
To play as Judecca, play the game for 300 hours.

Play as Master Gundam
To play as Master Gundam, beat Master Gundam in story mode three times and you will be able to select him in Story Mode.

Combo Battle when Master Gundam fights Shining Gundam
If you and your opponent both use the "finger" move at exactly the same time at a certain distance (Shining Finger or Master Gundam's Darkness Finger) the two moves will cancel each other out. When this happens Master Gundam and Shining Gundam will engage in a series of combos on each other while rising into the sky.

Super Mode Shining or Master Gundam
To access Super mode Shining Gundam pick Shining Gundam and any other opponent in VS. mode. Beat Shining Gundam 21 times in a row.After the 21 time press start on the joystick that Shining Gundam lost when choosing him for the 22 fight. You will here him say something in japanese confirming that the code works.
For super mode Master Gundam, follow the same instruction but he has to lose 31 times.

Choose Winning Pose
To choose a wining pose at the end of a match simply hold the L or R buttons at the end of the battle when the screen say K.O.