These things are people (in the way we understand the word).
Proteans or 'Olm'
These are virtually human, only about a million years old. Cave-salamander people. Long white bodies, seven feet tall and slender as a child. You could almost fit your hands around their waist. Elongated limbs with small child-like three fingered hands. Bright vibrant gill tufts like rose-head ruffs, Elizabethan punks. Slender tails.
Their faces are blank, eyeless and beautifully shaped. Red vertical nose-slits shiver open when they leave the water. Almost-lipless mouths that gawp a centimetre, showing sharp pinteeth and indecent pink tongues. They're kind of hot, but in a way you'll never mention to anybody else because they'll think your mental or perverted.
Bodies weave endlessly like slow sine waves from a dreaming mind. They appear to drift but they can feel movements in the air. Faces and bodies thick with invisible hypersensitivity.
As you swing your weapon towards them they drift aside. Like being impossibly dodged by an old old man. But if you can see, you have the advantage. In air count them as unarmoured. When they slip into the water, it's like gifting them an extra sense, AC as plate. The whole wrap of stream around them becomes another organ of discovery.
They have the same intelligence and emotional complexity as humans, but shaped by a dark world of endless famine and a braille-wise underculture of ultra-sensory contemplation.
They can learn and speak other languages. The only time you'll ever hear them is when they speak your tongue to trade, or the faint whistle-pitched mouth clicks of a war party as it emerges from the flow in the darkness.
They know what sight is and they are not stupid. They think about it the same way you and I think about allen keys or fishknives. Clearly very useful in a highly limited set of circumstances, but a fucking bitch to carry around with you and a poor use of resources. They will trade when necessary, or to accomplish sight-useful goals.
Protean reasons for trade:-
1 Identifying something in the distance of an airy space that cannot be climbed.
2 Chief has a new status-signifier-item, is meeting with sighted peoples, needs to know if the 'colours' have dignity. But you have to describe it in terms he can understand.
3 Bad air is killing us. Follow us through the area, watch your 'lantern' tell us if the flame changes 'colour'.
4 Games for the feast, stand ten meters away, we change position, and again, now tell us which one of us is which. HOW DO YOU DO THAT?!?!
5 Radical touch-bard needs new sense-words, is seriously angling for a classy new mate, needs to knock it out of the park at the great gathering, is willing to cross weird cultural boundaries to come up with stuff no-one has felt before.
6 Shaman saw colours after mushroom dream-flight, needs someone to talk him down, but no-one understands. Like Grant Morrison after he met the 5th dimensional aliens in Katmandu.
Imagine six gigantic fat translucent milky cells in a tube about five feet high. Then two stalks poking out the top. Each stalk made of three thinner cells in another tube, and where they meet at the top, a bunch of six foot antennae and some kind of boiled-egg sensory thing.
The Cambrimen were the first attempt of eukaryote cells at a human shape. But life didn't have enough genetic complexity to build anything good, so they ended up like this. They don't look like creepy primal cthuloid entities, they look fucking useless.
You can actually see the cell core floating around in there like a murky walnut. If you held in in your hands you'd feel your palms tickle as their crap analogue genes divided.
Pathetic, failed beings. Legs barely differentiated. If they stand still too long the legs grow back together. Just a stupid tube really. Chatter and wander around like fucking idiots. Nothing wants to eat them because their stupid giant cells just mash like jelly. Even oozes won't touch them. So so so hard to kill because simple makeup means no nervous system, so no trauma damage. No complex biological transmitters means no poison. Can't drown. Can't breath. Barely grows old. Has something like a pseudo-culture, like a subnormal child reading the back of a book upside down because it's seen you do it.
Attacks as a 1 HD monster. Has 5-8 HD. Takes hours and hours to kill as it flails at you uselessly.