Complete Sanctuary Time Attack mode under the indicated time limit to unlock alternate music at the title screen and an alternate character pointer.
Earn the "Best" ending.
Obtain Curly's Panties and save the game.
In the Plantation stage go to the "Rest Area" in this room go to the bottom where the water is, and go left through an opening in the wall until you reach an outside area called the "Inner Wall"* This place is dangerous and you will need the booster 2.0 for it. Struggle your way (and I mean STRUGGLE) to an area where you see a door at the bottom left but there is a wall between it, go under the wall and boost upward until you get to that door, once inside you will enter a "Secret Grave" with a huge "Prinny" statue at the center, examine the sparkly object to get the "Prinny Cap" this can be equipped over your existing cap. *Note* if you fall at anytime while in the Inner wall area its counted as a game over just like the "Outer Wall" stage, so make sure you save where you see the save points.
Time attack will be unlocked when you beat "Sacred Ground" stage. In time attack you can choose five of the six weapons and you can choose the number of health that you want. After that you can play the extra stage again.
Successfully complete the "Sacred Ground" level. In Time Attack mode, you will have a choice of five of the six weapons and can select how much health you have.
Complete the indicated task to obtain the corresponding weapon.