All weapons  -  Enter DLVTRKBWPS as a password. 

Alternate Ending  -  On level 9, press DOWN when you reach the area where your enemy appears (there's only one on the level.) If you do so you'll enter a secret tunnel. Shoot the computer and destroy the incubator to view a different ending.

Bird mode  -  Enter DLVTRKBBRD as a password. (To fly, hold Select during game play and press A.) 

Passwords  -  To play on a particular level, enter its corresponding password below.

Level Easy Medium Hard

2 DVYLWKVYYZ QVYLWKVYYC DLTLWKVYYC
3 GRYLWKWVVN TRYLWKWVYY GNYLWKWVPP
4 DRYLSRWVVZ QRYLSRWVPT DNYLSRWVPT
5 GVZLSRSQVV TRZLSRSQPS GLZLSRSVPW
6 DVZLBVSQQT QVZLBVSQVN DLZLBVSVVB
7 GRZLBVBQQQ TRZLBVBQVL GNZLBVBQVL
8 DRZLBVBQQT QRZLBVBQVN DNZLBVBQVN
9 GVYNBVBQWC TVYNBVBQQD GLYNBVBQQD

Playing Tips for Level 1
To complete the First Level:-  
Go through the store and into the alley. Run to the sparkling pile of rocks (on the side closest to you). From the enchanted rock pile you will obtain a knife. With the knife, use the select button to determine good guys from bad ones. (Foes are lizards.) 
Kill all of the lizard people, then go back to the starting point where a warp should have appeared. Enter the warp. 

Skip level  -  Enter DLVTRKBLVL as a password. (To skip the current level, pause the game and press A + B.) 

Start with 99 Arrows  -  To start a game with 99 arrows, you must kill the Raptor on Level 2. Then climb the first tree that you see and pick up the 1-Up. Keep walking through the stage picking up arrows for the bow. At the end of the stage, fall and die. Keep doing this until you have full ammunition for the weapon! 

Unlimited energy  -  Enter DLVTRKBNRG as a password. 

Unlimited lives  -  Enter DLVTRKBLVS as a password. 

Use Chain Gun on Level 2  -  To use the chain gun on the second level, you must first complete the code to use the Particle Accelerator on Level 1. This gives you the chain gun without ammo. To arm the chain gun, simply advance to Level 2 and grab the pistol! 

Use Particle Accelerator on Level 1  -  To use the Particle Accelerator in the first level, enter the password: QVZLBVSQLV. Play the game at medium difficulty, intentionally losing all of your lives. Reenter the password and do the same on the easy setting. Start a new game on easy and get the Light Burden. You should now have the Particle Accelerator! .