Giga Wing - Platform: Dreamcast

Play as Stranger:
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Enter the Gallery section and press 
B, X, Y, B, B, Y, X, B 
at the first screen. If you entered the code correctly, 
you will hear a sound. Alternately, successfully complete 
the game on any difficulty setting without using any continues.

Invincibility for player two:
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Select two player mode, and have player one select a jet. 
Then, press Start + A on controller two when selecting a 
jet for player two.