To do this you must first complete the rpg mode in all levels. When you meet the requirements for all levels you get to use Snork, Mufu, Udan, And Tori! Now i know this may be hard so here are some gameshark codes swipped from www.datel.co.uk.
Player 1 infinite health:-801EF996 0100
Player 2 infinite health:-801EF17DE 0100
Player 2 no health:-801F17DE 0000
Codes for Quest Mode (rpg)
Hyper Mode:-801F0390 0001
Maximum Strength:-801F141A 0100
Maximum Defense:-801F1418 0100
Maximum Molmoran:-801F11428 FFFF
Maximum Hearts:-801F141C 0003
Also To change the View Press and hold L2+R2 before your match starts...