Easy:

Level - Password
01: Treasure Island - Marvin Martian, Elmer Fudd, Daffy Duck
02: Crazy Town - Daffy Duck, Taz, Elmer Fudd
04: Space Station - Yosemite Sam, Daffy Duck, Elmer Fudd

Hard:

Level - Password
02: Crazy Town - Taz, Marvin Martian, Yosemite Sam
04: Space Station - Marvin Martian, Taz, Yosemite Sam