PASSWORDS

Press Alt+P to show the password box:
 
Start at Zone 2: znarf
Start at Zone 3: koonac
Start at Zone 4: elmtree
Start at Zone 5: glimaa
Start at Zone 6: youen
 
Hidden passwords (Revealed once you finish the game):
Watch ending: mionyx
Play deleted level: tuca 
MM3 poster: liskey