Where can I get information on mapper 74? Some guy on the pocketnes message board wants it emulated. I've seen source code for it in Virtuanes and Fceu, but I'd like documentation on it instead.
Google says
it's an MMC3 clone, as
you apparently know. I'd look for docs, but Kevin Horton's site seems to be down.
Given the description with both VROM and VRAM enabled, the mapper might be something like TQROM (iNES 119). The Wayback Machine has
Kevin's TQROM doc. Try looking at what a mapper 74 game writes to the CHR bankswitch registers when the graphics glitch.
Apparently, this is a combination of at least 3 different mappers, where selecting CHR bank 00/01 (for 256KB PRG games), 08/09 (for 512KB PRG games), or 1A/1B (for "Sugoro Quest - Dice no Senshitachi (As)") causes it to instead map in CHR RAM.
In my opinion, this is a 'lesser' mapper, only used to run poor quality Chinese hacks of existing Japanese games.