The whole argument on why Mystic Cave was called Dust Hill in the Wai proto is that it took the level slot of the desert zone and they hadn't updated the name yet. This doesn't make sense since the desert zone's level slot (03) still exists alongside Mystic Cave's slot (0B). If Mystic Cave didn't replace the desert zones's slot then why is it called Dust Hill? It makes more sense that Dust Hill was the proto name for Mystic Cave. Green Hill was Emerald Hill's proto name judging by the map and Emerald Hill did indeed replace Green Hill's slot (00) in the Wai proto. ID 01 was likely reserved for Ocean Wind Zone, just look at the internal order: 00 - Green Hill (Emerald Hill) 01 - Ocean Wind Zone (Labyrinth leftovers in NA proto) 02 - Wood(s) Zone 03 - Sand Shower Zone (desert) 04 - Metropolis Zone Fits the order of the present map, doesn't it? EDIT: - Also interesting: 09 - Rock World Zone (empty level slot) 0A - Oil Ocean Zone 0B - Dust Hill Zone (Mystic Cave) Fits the bad present map.