Play as GYN:
At the Options screen, set the difficulty to normal and choose 2 round mode. Now beat Story mode using any character. GYN is now playable.

GameShark Codes

Infinite Energy P1	d022671c0000
			8122671c00fa

Infinite Energy P2	d022671e0000
			8122671e00fa

Infinite Time		d02267240000
			81226724003c

1 Win To Win P1		d02267150000
			802267150001

P1 Never Wins		d02267150001
			802267150000

1 Win To Win P2		d02267170000
			802267170001

P2 Never Wins		d02267170001
			802267170000

GS Button For		8922671c0000
Death Blow P1		8922671e0000
			

Thanks to Revolution readers Ernie Rodriguez and Young!