At the Options screen quickly press A, B, C, C, B, A. If done correctly the screen will flash. You'll have to look closely, though; Shaq and crew are not heavy bleeders.
Character Select
To play any character in Story mode, go to the Options screen and enter a number from the list below:
On the first island, go to the lower right-hand corner, walk down the stairs and press Start to fight Beast.
Fight Beast's Skeleton Army
On world two move to the upper right corner and press C.
Fight Mephis
On the second island, go to the southern end of the island and find the fence. Go to the middle of it and press Start to fight Mephis.
Fight Sett's Clone
After beating all people on the first land mass, cross the brige at the bottom of the next land mass. There are two poles. Go between them and press start to fight Sett's clone.
Play As Beast's Skeleton
At the option screen press A, A, A, C, C, A, A, B, C, B.
Third Bonus Stage
In Story Mode, head to the rightmost trees above Kaori's Catwalk Falls (essentialy, the top right corner of the landmark) and press Start. There, you will reach a bonus stage, in which you must smash a number of skeletons before the time runs out. Getting a perfect score will earn you an extra continue.
Blood...