INES Mapper 054
Nestopia's source claims that iNES Mapper 054 was allocated for the board containing the multicart Novel Diamond 9999999-in-1. However, its implementation is what Disch's notes say for iNES Mapper 201.
(In turn, Nestopia's implementation of mapper 201 is halfway between what Disch's notes say for m201 and iNES Mapper 226)
GoodNES 3.1.4 and FCEUX 2.2.2 have nothing allocated to mapper 54, and only have Novel Diamond as a UNIF dump with MAPR "BMC-NovelDiamond9999999in1".