Acephali or Blemmye are among the human-like mythoogical creatures that seem to get little love in RPGs. RuneQuest 6/Mythras has stats for them, and its recent supplement Mythic Constantinople even features them as one of the major non-human races; but that seems to be it.
I really like them because while they seem excessively weird, they still seem to make sense on a fundamental level. You can imagine humanoid creatures with their eyes, noses and mouths in their chest as something that, in terms of a made-up biology, might actually work. (It would be much harder with, say, the Sciapods).
A while ago, I took the core concept of the acephali and tried to spice it up a little for a guest spot in my Numenera campaign; these creatures, as outlined below, are also part of my ever-changing heartbreaker setting. Except for the face-in-the-chest thing, they have very little in common with the Acephali/Blemmye of myth; but still, I like to call them that.
No stats - I used them as NPCs for Numenera, where you practically don't need NPC stats. If anyone feels like statting these guys up for one system or the other, I'd be most honored!
The closer you get to a moss-eyed acephalus, the less human he or she will seem - that starts with the he or she thing, because the Acephali have no discernible biological sex. From afar, they might look like skinny humans without heads, a greenish pair of eyes where a human would have his nipples, two nostrils and a broad slit of a mouth beneath them. Getting closer, you'll notice their three-fingered, nailless hands and feet and the fact that their eyes are not actually eyes. They are two big, dark-green blotchs of a kind of short bushy hair, frayed circles with small white spots in the middle. When they open their mouths to speak in their slow, high-pitched voice, you'll also notice their many small, rounded teeth and the two shorter extra tongues nested below their big, long main tongue. Their gums are dark gray, as is their blood.
There "eyes" are actually a type of lichen, with which the naturally eye-less acephali have entered a most beneficial symbiosis. The light-sensitive lichen grant the acephali the power of sight, while the Acephali serve to carry the lichen around to ever new habitats.
It is a matter of speculation whether the lichen drive the Acephali to roam or whether it is historical and social circumstandes that have made them a people of the road. Acephali tend to roam around in large family groups, sooner or later settling down with other races, often to move on two or three generations later. Usually, they are met friendly, but with a certain distrust, because while they bring many valuable skills with them, they are also considered fundamentally alien by most humans and similar species.
While they Acephali's sight is poor - they are all colorblind and bad at making out things that don't move -, they have an extremely developed sense of taste and smell. That makes them valuable as alchemists (or, due to discrimination, as servants for alchemists). They also have an iron stomach, especially when it comes to plants, which is mainly due to their ability to consciously transform substances that are poisonous to them by changing the chemical properties of their saliva. An acephali food taster can not only tell you which specific poison has been used in an assasination attempt, he or she is also re-usable.
Regarding the Acephali's sex and gender: That seems to be something that is not talked about to outsiders. Their genitals are hidden away in skin pouches between their legs (or so humans suppose). These are usually quite visible, since most acephali wear little or no clothes if the climate permits (they are are slightly less susceptible to heat or cold than humans). They don't seem to make any social gender distinctions, and since they tend to live in large families of about a dozen individuals, both adults and children, that doesn't provide much of a clue either. It seems that most acephali are able to carry children, which are born after five months. These children are smaller and even more helpess than human babies. Usually, they don't receive their lichen "eyes" before their fifth birthday, when they are considered ready to deal with this new kind of sensory input.