[NES] Splatterworld prototype (mapper 210, submapper 1) rendering issues

Summary

Rather than trying to describe the issue, a picture speaks a thousand words, so here are some screenshots, comparing Bizhawk 2.11 against Mesen 2.1.1 which renders the game correctly. All three NES cores included in Bizhawk exhibit the same issue.

Output/screenshots

Bizhawk 2.11:

Mesen:

Bizhawk 2.11:

Mesen:

Bizhawk 2.11:

Mesen:

Bizhawk 2.11:

Mesen:

Rom Information

game
  sha256: 83c73897873109f86b1cdd4dd1a7d3c57085e46e5ab491be31037cfdf47a76ad
  name:   Splatterworld (English v1.1)
  title:  Splatterworld (English v1.1)
  region: NTSC-J, NTSC-U
  system: Regular
  board:  NAMCO-340
    chip type=340
    memory
      type: ROM
      size: 0x10
      content: iNES
      data: 4e 45 53 1a 20 20 23 d8 10 00 70 00 00 00 00 01
    memory
      type: ROM
      size: 0x80000
      content: Program
    memory
      type: RAM
      size: 0x2000
      content: Save
    memory
      type: ROM
      size: 0x40000
      content: Character

This prototype was released to the public last Halloween. Some links to info on the game and its fan translation:
https://splatterhouse.kontek.net/famicom2.html
https://aeongenesis.net/projects/splatterworld
https://romhack.ing/database/content/entry/uz8qKfAyQo2GkTX_DHwt6g/splatterworld-english-translation

Part of the readme from the translation by Aeon Genesis with additional info:

Several versions of the ROM with different headers are floating around on the internet. This patch should work on all of them, and *hopefully* will correct their headers; reference the checksum information at the end of this readme. The ROM should be mapper 210, submapper 1. This is the correct header:

4E 45 53 1A 10 20 23 D8 10 00 70 00 00 00 00 01

(Mapper 210, submapper 1. 256K PRG, 256K CHR, 8KB SRAM, battery. Vertical mirroring.)

Note that the patch expands the ROM to have 512K PRG; your header should look like this after patching:

4E 45 53 1A 20 20 23 D8 10 00 70 00 00 00 00 01

This mapper is not widely supported, however it has been tested and is working on the Mesen 2 emulator and on FCEUX. At the time of writing, the Everdrive N8 Pro *does not* correctly support this mapper, even though it claims to do so.

In short:

TESTED AND WORKING:    Mesen2, FCEUX
NOT WORKING CURRENTLY: Everdrive N8 Pro

Host env.

• BizHawk 2.11; CachyOS/Arch; NVIDIA

Start by reproducing Splatterworld (English v1.1) in BizHawk 2.11 and comparing all three NES cores with Mesen 2.1.1. Investigate mapper 210, submapper 1, and the differing rendering output; done means the game renders like the supplied Mesen reference images.