After 1966 movie Mondo Bizarro (literally "Bizarre World" but interpreted as "very bizarre"), where mondo is from the 1961 Italian movie Mondo Cane (A Dog's World) and reinterpreted as an intensifier.
"As Asia's productivity shakes the world, and as `just in time' inventory management keeps rolling along, air cargo has become one mondo important gig." — Ed Stephens Jr.; Cargo Tells a Story; Saipan Tribune (North Mariana Islands); Jun 3, 2005.
Also, now that I think about it, "Mondo Ghost Dome" would be an awesomely fitting name for the final level of Area 4 in my hack (and a neat reference), as it's both a haunted and a metallic/machinery area. I could have it as a giant metal dome with ghosts and lots of puzzles and riddles for the player to solve. I knew I needed something more evocative than "King Boo's Haunt".