Alternate endings:
Unlock the following endings by performing the corresponding actions:

Bad ending – Leave with Kazuma in the Egg Corridor.
Good ending – Complete the Sacred Grounds area.
Normal ending – Complete the escape sequence after the final boss without going through the Sacred Grounds.

Chaco’s Lipstick:
After talking with Chaco about the Jellyfish Juice, rest in her bed. When you wake up, her lipstick will be in your inventory.

Get Jet Pack earlier:
The Machine Gun can be used as a “jet pack” at Level 3. Just jump and aim it downward to float up until you’re out of ammo..

Obtaining the Spur:
Once you get to Curly and beat her in the Sand Zone, don’t trade your Polar Star for the Machine Gun. You can later trade it for the Spur; the strongest weapon in the game.