Full pause screen:
Pause game play, then press X + Y. 

Fight as Pride:
Successfully complete basic mode with seven different characters. He looks like an
old Fokker but has different moves. 

Fight as Mel:
Successfully complete basic mode with eight different characters. She is the girl from
shop mode and fights similarly to Julia.

Unlocking the options in the Extra Option Menu:
Every time basic mode is cleared with a different character a new option will be
unlocked, until the extra option menu is full.

Extra Arenas:
After basic mode has been cleared with all the default characters, as well as Mel and
Pride, three new arenas exclusive to original mode will be unlocked. To access them,
move the pointer left or right at the arena selection screen until it is off-screen. A large
box with the "Extra Arena" message will appear. Select the desired extra arena. The
arenas are a small room, a very narrow bridge over along drop, and a geometric
(cubes stacked in weird patterns) arena. 

100,000 Credits for shop mode:
If during the course of the game you manage to pick up item # 103, which resembles
red turban, sell it for 100,000 credits. This item seems to appear randomly.