To a certain extent, orcs and goblins were created so that we could have killable humanoids. The entire species even had an alignment of Chaotic, which meant they were intrinsically antithetical to all that was good and decent in the world.
This is good, since it allows us to stop worrying about morality and instead just focus on the best way to kill those bestial, cruel, dishonorable orcs and take their treasure. We can use anti-human tactics without actually killing humans. Orcs are raiders and warlords, rarely adventurers or city-builders. Many people don't like a lot of morality in their games; they want to be heroes.
But this is also bad, since dealing with trad orcs becomes a one-dimensial exercise. Orcs are evil, violent, stupid, greedy, and dishonorable. Their actions become predictable, and they become too shallow to hold much human drama or plots. It becomes very easy to kill orcs on sight. Compared this to human bandits, where PCs are much more likely to talk to them first, or to be interested in their relationships and history (+James Young taught me this).
Anyway, you don't have to open very many sourcebooks to find weird, bestial humanoids to kill. But it's a bit harder to find monstrous races that are human. I don't mean human in the biological sense, but monstrous races that PCs will be inclined to treat like people. (Coincidentally, sci fi is filled with monstrous races that get treated like people.) Anyway, here are my attempts at more human monsters.
They build honeycomb cities in caves and behind waterfalls. Their corpses appear exactly like human albinos. However, their viscera differ, and it is impossible to cut one open and not notice the daisy-chained kidneys nor the pale, gossamer-winged arches of their tubular heart.
The orcs believe that an ethrum's organs, by virtue of their auspicious appearances, are of cosmic significance. Orcish haruspices will pay huge prices for a live ethrum, since they believe that a haruspex will enjoy vastly superior divinations by using an ethrum.
While alive, they are truly invisible. No light touches them, and conversely, they are blind. They sense their environment through echolocation. Each man or woman, made directly by their epiglottis, and they communicate with the same noises. Each has a singular, specific, percussive syllable that they use for echolocation (to distinguish their clicks from their peers) that also doubles as their name.
They can learn to understand Common as easily as any other race, but can only speak it in whispers.
If injured, their blood appears after a few seconds, as red and as wet as any humans. If killed, their body fades into invisibility over the course of a few seconds. It is said that the veil of invisibility parts for them in their last moments, and they briefly glimps the visible world in the moments before death.
They wear nothing except harnesses, made so that they can be dropped at a moment's notice. In combat, they discard their harnesses and fight with either their bare fists (many of them are excellent wrestlers) or with stilettos, so thin as to be almost invisible themselves.
Their cities are small, secretive affairs. Their farms are fruit orchards, fisheries, and thin-stalked rice that they grow in the shallow water. Their books are tortoise-shells filled with dense and complicated patterns of finely drilled holes. Their women sing songful epics, beyond the boundary of conscious perception, but within subconsious recognition. Humans are affected by these songs and are transported by its mood, although they will not realize that they are hearing it. While traveling, they eat rice balls, usually filled with fish meat, waterfowl, or fruit.
PCs may discover an Ethrum as a (painted) wrestler in a coliseum, as a hostage in an orcish encampment, or as raiders. Like vikings, many of them have warrior traditions that involve going on long, secret raids against settlements. A band of ethrum warrirors will sometimes go on a single, vast raid that lasts a season or more.
The Huntresses of Zao (rhymes with "say oh")
These warrior women hail from the lands around Lake Zao, a body of water whose contours are perfectly hemispherical. Their skin is lime green and smooth in one direction while rough in the other, like a shark's. Their hair is red or white or ghostly green. Their hair is huge and voluminous. They are tall and statuesque.
They are beast riders. Away from her homelands, you will never encounter a Huntress on foot. She will be riding a giant gecko, terror bird, or maned serpent.
Their menfolk are never encountered. It is said that they stay behind in their dome shaped houses, tending the burgundy eggs that their wives lay.
They drink black wine and eat raw eggs. They sleep in trees, slumped in the branches like exhausted cats. When one of them dies, they recover the body and feed it to the deceased's mount. (This is one reason why they prefer carnivorous mounts.) They paint the animal in her blood, and then turn it loose. So if you ever see a blood-covered horse staring at you across a meadow, now you know.
They serve the dragon-sorcerer who is called Tar Lath Lien. He has charmed them, dominated them through their generations. They love him, adore him. But at the same time, they know that this love is the product of an enchantment. They know that their love for him is false, but they the strength of the enchantment is such that they cannot resent him for it. Why should they love him, when he is aloof, and callous, and sometimes cruel? How can they feel anything except love for him? And since they are incapable of resenting neither Tar Lath Lien nor the enchantment, the anger and frustration spills out onto themselves. They feel guilty, frustrated, and angry for reasons that they can't articulate. All they know is that they love Tar Lath Lien, and would do anything to make him happy.
For his part, Tar Lath Lien uses the huntresses to guard his borders. Since very few people are dumb enough to fuck with a sorcerer-dragon-king and his amazons, their defense is often reinforced and rarely tested. Due to this quietude, Tar Lath Lien will often send his huntresses out into the world to let off some steam. He knows that his enchantment is a heavy one, and the stress of such a large cognitive dissonance, for so long, for so many cannot be endured.
While wandering the world, the huntresses look to engage in heroic violence as often as possible. Their code of honor allows them to attack anyone who is carrying a weapon. However, they can never use a larger or more deadly weapon than their target, nor can they wear armor if their target is wearing none. According to their rules of combat, the victor of the fight chooses the punishment that the loser will recieve. This is usually "run them off naked and covered in bruises", but if there has been any rudeness or escalation, they don't mind killing people.
They're just as likely to seek out the bulette that's been menacing town as they are to attack merchants, trounce the guards, and steal all the money (which they will then use to throw a private party in the woods).
Every huntress has a small blue jay that nests inside her. When she is killed, the blue jay will immediately fly from her mouth and fly back to Lake Zaotan. The bird will seek the deceased's next of kin and alight on their shoulder. Then the bird will speak in the voice of the dead woman, telling all of the circumstances of her death, including accurate descriptions of all relevant parties. After several minutes, when the speech is concluded, the bird will drop dead.
When they are allowed to medicate themselves, and balance their humors, they resemble blond humans with a single red eye.
When they are denied the treatment that they need, they degenerate. Their chests become sunken, and eventually completely invert, creating a hole through their chest large enough for you to stick your hand through. Their red eye enlarges. They tend to collect fat in a pot belly.
Nearly every Ostrogaunt is degenerate.
They have odd hips, and although they can walk, they cannot run. Instead, they hop by hyperextending their knees, which makes it look like their legs are bending backwards. This leads to their nickname of "jumpies", or more frequently, "jumbies".
Most of the superstitions about them involve walking backwards, e.g. "jumbies can't steal you outta your bed if you walk into your bedroom backwards".
They also drink blood. Not because of a biological compulsion, but a cultural one. They'll pop a hole in their cow's neck and drink a quick pint when they want refreshment. If they spot a goat herd during a midnight constitutional, they might open one up with a thumb dagger and drain it dry.
They do not come from our dimension, and in fact there is no record of them beyond a couple hundred years ago. While there are a few small, scattered colonies of them, evidence suggests that small groups of them are constantly arriving in our dimension through unknown means, an intermittent-but-still-constant flow of accidental immigrants. They say that they come from a place called Capricavena, where they served and feared creatures that they call Vor-Gulai. The Church of Hesaya refers to them as "Type IV demons". But none of that really matters.
Every Ostrogaunt is dying. Our dimension is toxic to them. They call it "falling down". It is a path of madness and mutation that will claim their minds and memories before it claims their bodies. The first mutation that claims them is the creation of a hole in the center of their chest, large enough to throw a pingpong ball through. Between the skeletal re-arrangement and pulmonary compression, it is a very painful process. Ostrogaunts are fond of saying "The void is filled with fire", which is sort of a euphemism for "life sucks; I don't care".
There is a cure for the Fall: human brains. Or actually, cerebrospinal fluid. Enough cerebrospinal fluid can halt or even reverse the gradual decay of their bodies and minds. Animal brains can slow the process, but a long-term solution requires the sacrifice of sentient creatures.
The prefer to extract cerebrospinal fluid into clear elixirs (for health reasons--humans can be unsanitary), but if a ostrogaunt is desperate or in pain (if his void is filled with fire) they're not above smashing your head in with a rock and lapping up the juices, even in the middle of combat.
Primitive or lone ostrogaunts will operate at the fringes of human society: preying on cattle (draining their blood). Some of them also manage stirge colonies (which may share a background with the naus-garant.)
Larger, established ostrogaunt colonies have even been begun imprisoning humans (or other sentient species) and draining
Ostrogaunts are not unethical creatures. Their justifications range from the pleading "would you rather my children go insane and die?" to the apologetic "it is only until we figure out a way to go home" to the defensive "only ostrogaunts can judge ostrogaunts".
But many ostrogaunts are uneasy with this method of survival. There is evidence that they have spent a considerable amount of time researching an alchemical substitute for human CSF. And in one recorded instance, a young ostrogaunt girl was so overcome with guilt that she helped three human prisoners escape. When the three humans reached society, they described where they had been held captive by the ostrogaunts, and a small army was dispatched to raze their enclave to the ground and slay every last ostrogaunt. Because humans will do what they must to survive, too.
Ostrogauntts are masters of alchemy. Many of their alchemical feats cannot be reproduced by their best human counterparts. Absolute savants.
They can transform their children into monsters by giving them certain alchemical elixirs. Since these potions work by shaping and molding the mutation process, they will not work on humans (though they might give you tumors). Ostrogaunts are still discovering these elixirs, and different colonies will trade recipes between themselves. In a world without birth control, turning your newborn into a monster is seen as more humane than killing them or subjecting them to a life of constant homicide. And it has the additional advantage of giving the colony a new protector.
The most well-known of these teratomorphs is called the Ostro-Karkarai, an amphibious creature that resembles a 20' long eel with a toothy horse-head and long, agile legs, like a greyhound's. It's a stable mutation (i.e. unlikely to suffer secondary mutations, unlike some of their other creations) and it retains enough of its intelligence to acknowledge its name, recognize its family, and join that at the dinner table for important meals.
Ostrogaunts worship (obey?) a god (intelligence?) that they call the Red Voice, the Great Engineer, or the Operator, which claims to have arrived on Centerra only a few decades ago. It is a real thing, since it can apparently speak to anyone who drinks a certain potion, that they call Yesterday's Wine. Ostrogaunts use this to coordinate their actions across the continent.
The Red Voice instructs them to build strange structures in the Gray Waste and in the Frothplains. None of these are completed, but many believe that they will be some sort of portal upon completion. The Voice also instructs them to build strange weapons, like daggers that shed a metallic "skin" inside their target, which then shatters into hundreds of glassy shards. Or the lightning guns. None of these weapons function in the hands of non-Ostrogaunts.
this video contains lightning guns
Very loosely: the Ethrum are based on drow, the Huntresses of Zao are based on orcs, and the Naus-Garants are based on mind-flayers.