We're finishing up our quick tour of the mainstay, low level humanoids with gnolls. There are others in the Monster Manual and plenty more in the D&D universe, but goblinoids, orcs, kobolds, and gnolls are the usual suspects, at least in my head cannon. And of that list gnolls are the most brutal. They're also the only ones that don't speak common, they only use their own, rudimentary language, so you won't be persuading, negotiating, or bribing these creatures. The options pretty much boil down to fight or flight.
The story goes that Gnolls are what happened when a pack of hyenas scavenged the corpses left in the wake of the demon lord of destruction Yeenoghu last time he got out of the Abyss. Every race has their origin story of course but few are as punchy and defining. Gnolls are all bestial savagery twisted by demonic influence. They have an insatiable hunger for the flesh of intelligent species, and roam the world in packs and war bands causing destruction and devastation. Their Rampage features marries nicely with this, if you want to make Gnolls extra scary in combat have them taking a bite out of anyone they drop to zero, instead of moving and attacking a new target, because that's two failed death saves. Scary stuff. Also, keep in mind they attack the weakest targets first; they like killing not fighting.
Volo's Guide to Monsters does some expanding, and gives us the tidbit that gnolls will eat each other too if they've gone too long without a meal. No big deal though, because there's a good chance this will just lead to undead gnoll witherlings. We also get the Flind, which is a gnoll leader with a super cool magic demon-powered flail; though it's a huge jump to CR9 so feel free to scale it down or split it into three for lower level adventure. We also get a table with a laundry list of demons to invite along to the war band if we're making gnoll themed adventures. And they are certainly a great starting point if your aiming your campaign towards the Abyss.
But I would also consider Gnolls an excellent candidate for a complicating third party. Almost more a force of nature that both the party and their adversaries have to contend with. Sure we can do black and white or shades of gray, but why not both at once? We can have good and maybe evil and really, definitely evil; Break up the binary.
Maybe the war between the goblins and kobolds doesn't seem like a problem to the PCs until gnolls start spawning in the aftermath of the battles. Or have the party come over the hill and see gnolls attacking an orc camp. Are the players going to intervene or watch? I bet they hang back, then explore the aftermath. That's a great opportunity for a DM to show that the Gnolls aren't like other humanoids, they don't care about treasure. “It appears they took all the weapons and armor but left the gold and gems just lying around.”
Throw in another complication: Maybe a group of bandits are stealthily tracking the warband for this very reason and feel like this is rightfully their loot, and they want to get it and get out before the hyenas on the edges scavenging the dead eat enough to literally explode and become full on Gnolls themselves. Intense.
