Invincibility:
While playing, hold Right then press Square, Circle, Circle, Circle, Square, Circle, Triangle, X.
Level Select:
While playing, hold Right then press Circle, Circle, Square, Triangle, Triangle, Square, Circle, X.
Weapon Upgrade:
While playing, hold Right then press Square, Square, Triangle, Triangle, Circle, Circle, Circle, X.
Skeleton Zeke:
Before the copyright screen at start-up, hold Circle, Square, X, Y.
Invisible Zeke:
Before the copyright screen at start-up, hold X + Square + L1 + R1.
Features:
FAQ/Walkthrough v0.990.