Properties of Mapper 78:
- 16k PRG swapping @ $8000
- 8k CHR swapping
- Mirroring control (either H/V or 1-screen -- varies from game to game -- this is one of those sloppy iNES numbers where incompatible mappers share the same mapper number)

Properties of mapper 2:
- 16k PRG swapping @ $8000


Mapper 2 does not have CHR swapping -- and generally only has CHR-RAM.  Holy Diver uses CHR-ROM -- so it totally will not work with Mapper 2.  Plus there's a lack of mirroring control on mapper 2.

-- These mappers are incompatible --

The only thing that will work is the PRG because they swap the same way (and with the same bits of the same reg).  So games will run -- but they will be scrambled graphically.


If FCEU is running this hack -- it might be "autocorrecting" the header back to mapper 78 before it actually emulates it.  There is no way Holy Diver will run properly on mapper 2.


May I ask why you even need to change the mapper?  I mean if you don't even understand what the mapper does -- how is changing it of any benefit to you?


EDIT

also....


When most emus screw your hack up -- that's usually a pretty good indication that your hack isn't quite right.