Enemy's vital meter
To check how much vitality your enemy has (not Bosses), check the color of its level indicator. Vitality ranges from high (light blue) to low (red).

Full health and ammo
Pause the game and press L1(2), L2(2), L1, R1, L1, R1, R2, R1.

Versus mode: Unlock all characters and levels
Beat the game on easy mode with a D rating or higher.

Versus mode
Complete the game on any difficulty setting to unlock versus mode with five frames and most stages. Complete the game on any difficulty setting two times to get the remaining two frames and stages.

Alternate ending music
Complete the game on any difficulty setting and get an A-rank on all five rescue missions to get a different ending theme while the end credits are playing