Faolyn
(she/her)
Some of the stuff in Volo's seems to indicate that it's almost more like they're possessed than anything else. The sidebar with the guy who lopped off the gnoll's limbs and it kept going--it felt to me like the animating force was something apart from the actual body.Nah dude, even with the Volo’s Guide lore, I think the notion that they’re incapable of being good to be bollocks. “They’re hyenas mutated by eating demon-tainted flesh” doesn’t explain why they wouldn’t be able to be good. Either they’re driven by instinct (in which case they should be Unaligned), or they’re capable of rational thought (in which case they should be capable of Good.)
Which, in and of itself, is a cool and horrific idea. People eat this tainted flesh, which causes a parasitic demon to grow within them and take over. They become effectively rage zombies because of it, but they retain enough of their mind so that they can make decisions and form semi-cohesive groups, and the demonic aspect focuses the rage in a way that suits Yeenoghu.
Having it limited to gnolls only is dumb, though. Even in that sidebar, the guy "caught" the gnoll's madness and became a cultist. This should be an effect that can spread regardless of race, maybe by sneaking the demon-tainted meat into other people's diets or using it to pollute wells. Gnolls could still be Yeenoghu's favored race (maybe he made them before he became an Archfiend, or maybe he just likes hyenas), but this would allow for lots of gnolls, maybe even a majority of them, to be free of this curse.