Type these codes in the pause screen:

Invincibillity-b,a,r,c-up+c-down,z

Unlimited ammo-z,c-right,b,a,r,z

All guns-a,z,c-left+z,l,a

Easier enemys-a,b,r,lc-up+c-left

After each cheat do this code to comfirm it:

l+r(x20)

After u have comfirmed each code you should hear a chipmunk say-"Right on boys and girls"