There are two known versions of
Bio Hazard from Waixing: a regular version using Mapper 15, and a version found among Waixing's downloadable NES games using Mapper 227. The Mapper 227 version works flawlessly in emulators that support this mapper, while the Mapper 15 version will sooner or later freeze, usually early in the game. (There is also a differently-named version from Henge Dianzi which again uses a completely different mapper.)
I investigated the issue and found that the Mapper 15 version is just a mapper hack of the mapper 227 version. The bankswitching code appears at the start of every 32 KiB bank, and this is the only place where the two versions differ. Mapper 15's bankswitching code takes fewer bytes (17) than Mapper 227's, and after those 17 bytes in the Mapper 15 version, there are the remnants of Mapper 227's bankswitching code. This proves that the Mapper 15 version must be a (bad) mapper hack, and that the Mapper 227 version is the original version.
I further found that all Waixing mapper 15 ROM images are mapper hacks, judging by the fact that in each of these games, the Mapper 15 bankswitching code is followed by now-unreachable remnants of bankswitching code for a different mapper:
- 笑傲江湖 (Xiào ào Jiānghú)
- 爆笑三國 (Bàoxiào Sānguó)
- 外星戰士2 (Wàixīng Zhànshì 2)
- 上海大亨 - Shanghai Tycoon
Waixing's downloadable games include the original unhacked version of
Xiào ào Jiānghú as well. The other three are not available in their original unhacked versions: while the games are of course downloadable as well, the downloadable versions have been greatly modified from their original cartridge releases. This means that
Bàoxiào Sānguó,
Wàixīng Zhànshì 2 and
Shanghai Tycoon need to be redumped. I think their original mapper must have been 227 as well, though it can only be said with certainty once one tries actually dumping one of these cartridges.