Final Boss 
Enter this code at the Password Screen 
Password Effect
5DBY3MT8 Final Level: Scooby V.S. Masked Guy
Alternative ending password 
After you beat the game, you will be asked for a code (you had to see the movie for the code) 
Password Effect
SD2 Alternate ending
Level passwords 
Enter these codes in the Password screen. Password Effect
SDBY3MT4 level 5.4
4DBY3MK4 level 5.3
SBBY3MF4 level 5.2
4BBY3MC4 level 5.1
SDG7KMB4 level 4.4
4DG7KMBL level 4.3
SBG7KCBL level 4.2
4BG7KCBL level 4.1
SDB7KCBL level 3.4
4DB7KVBL level 3.3
MBB7KVBL level 3.2
LBB?TVBB level 3.1
MDGYFVBB level 2.4
LDGYCVBC level 2.3
MBC3BVBC level 2.2
LBCKBBBF level 2.1
CDBFBBBD level 1.4
CBBCBBBB level 1.2
BDBFBBBC level 1.3