Forest level fires
Get a bazooka, then find a location in the forest where there is a small gap between some trees. Shoot straight, without hitting a tree. Three or four trees will ignite even though the shot missed them.
Various Cheats
Enter any of the following "Passwords" as a password:
DNSTHMN = Level Select
NSRLS = Weapons
MMRTL = Invincibility
MMLVSRM = Max Ammo
CNTN = Unlimited Continues
DNLVSHSF = Invisibility
THDTST = Test Info
LVNGLRG = Living Large
DRVLLVSMM = Mini Mode
TNSLDRS = Tin Soldier
BGGRN = Big Green One
GRNGRLRX = Vikki
PLSTRLVSVG = Plastro
SHRMNSLDR = Hail Mendheimicus