The ROM is heavily encrypted for whatever reason; it's effectively a combination between how the NX-85 and the Pac-Man Pocket Player are coded, both of which had unique forms of protection. Here is a decoded copy, created using the EEPROM Pin Swapper (swapping bytes D0 and D1) and the byte-swapping Python code used for the Pocket Player. I haven't tested it fully yet but it seems to work fine.