NES 2.0 Mapper 261

NES 2.0 Mapper 261 was assigned by FCEUX for the 200-in-1 - Elfland multicart. Its UNIF board name is BMC-810544-C-A1.

Address latch

A~1... ..PP PmpM CCCC
         || |||| ++++- Select 8 KiB CHR-ROM bank at PPU $0000-$1FFF
         || |||+------ Select nametable mirroring type
         || |||         0: Vertical
         || |||         1: Horizontal
         || ||+------- Lowest bit of 16 KiB PRG-ROM bank number
         || ||         at CPU $8000-$BFFF/$C000-$FFF in NROM-128 mode
         || |+-------- PRG-ROM banking mode
         || |           0: NROM-128 (16 KiB PRG-ROM at $8000-$BFFF, mirrored)
         || |           1: NROM-256 (32 KiB PRG-ROM at $8000-$FFFF)
         ++-+--------- Select 32 KiB CHR-ROM bank in NROM-256 mode/
                       bits 1-3 of 16 KiB PRG-ROM bank in NROM-128 mode

The first game on that multicart, Elfland, is actually a CNROM game that writes to the multicart address latch to switch CHR-ROM banks.