There is a new mapper called the MXM-1. With this mapper you are allowed more tiles than a normal NES game and you can bank switch all the time swapping in new graphics constantly. Once that documentation comes out, do a version of Slaughter with this new mapper and then you will have something looking very nice on the NES.
Part of what got this project rolling was bickering with the Former Dawn guys on reddit. They took a weird stance on what qualifies as a "real" NES game. They use the MXM-1 for gigabytes of full-motion video... but think pass-through audio like on Famicom would be cheating. If you push people about their add-on chips, they tend to end up going, 'if a Raspberry Pi streaming Mario 64 doesn't count, neither do battery-backed saves!' So I said: okay.
This game is NROM. There is no mapper. You could swap its chip for Super Mario Bros. (Or the much better-looking Micro Mages.) I doubt anyone involved still cares about that argument, but I consider the point made.