The Green Sutras laid out a very simple magical spell, to draw the tormented souls of lower life forms back into their decaying corpses and force them into servitude. While such an act is vile, and deserving of the most critical punishment if performed against one of the Elfin blood, there is no reason to not use something so simple, versatile and useful on those of lesser pedigree and mongrel breeding.
The Nind Tah'Siltrin are the reanimated corpses of humanoid creatures, typically of the goblin or orkish races, but there have been dwarves, humans, and a sundry grouping of other races raised in such a fashion. The procedure to create a Nind Tah'Siltrin is direct, and involves 'dressing' the carcass of the victim to be raised in much a similar fashion to cleaning the carcass of a slain deer. The internals are removed, the corpse is drained of blood, and it is ritually skinned and flayed down to the bone. The ligaments holding everything together are left, as in time these will simply fray and fall off, and during the animation process, they help hold the incomplete Nind together. After a suitable amount of time, a Nind is nothing more than a skeleton, dressed in a few rotting tatters of flesh.
Much of the process behind their creature is curious. Lacking internal organs, the Nind should not be able to feel hunger, but they are voracious eaters. Rather oddly, the flesh 'consumed' by them putrefies within minutes of having been 'eaten'. As skeletons, what they ape at consuming is ripped apart, roughly masticated, and falls from the bottom of the skull onto the ground. As such, most active Nind will have dried blood on them.
Nind also tend to be armed, and after taking down a group of intruders, or enemies, the skeletal minions will strip them of their belongings, devour their flesh, and then take their gear and weapons as their own. Established older groups of Nind will be found wearing armor, carrying weapons and shields, and acting in a general coordinated fashion.
As far as undead go, the Nind are not exceptional. They have the typical abilities of lower end necromantic constructs. They are immune to fear, illusions and charms are ineffective against them, and they take a reduced amount of damage from edged weapons and archery is worthless against them. There is no flesh to harm.
They retain some spark of their old life, and as such, Nind will retain some skills the corpse had in its previous existence as a living being. A soldier would retain the ability to use weapons and make plans, while the hunter or archer would still find a way to string a bow and shoot arrows at foes. Thus the Nind are vastly superior to conventional skeleton soldiers in that they have a degree of skill to go with their bag of immunities.
Being drawn not from typical necromantic sources, the Nind are very vulnerable to Clerical magic, especially the domains strongly associated with solar deities, and magic spells, arcane and clerical, that call upon flame. They are quickly consumed and destroyed by said flames, and while unable to feel fear a holy man can smite them, and cause them to collapse into permanent death.
The Nind are hateful, and voracious. They will consume elfin flesh first above all things, followed by that of mixed blood elves. Such is their hate of those who create them. This is something that can used to an advantage as the Nind will make any elves their preferred targets and as such can be lured into traps, ambushes, and otherwise outwitted by the brave and foolhardy.
The Elves haven't always been the kindly whimsical protectors of the forest that most people know them as. Once they ruled the world, and they made war on everything that wasn't within their domain. They made war upon each other, as there were many different kinds of elves then, elves with antlers, and elves with strange colored skin, and elves of sizes and shapes like you could not imagine. They fought each other, or hid from each other, they made pacts with the old races, they swore fealty to the ancient ones and the new gods, and it was a terrible time.
It was then that a group of dark elves, not dark of skin, but dark of heart, sought the secrets of life and death and discovered the black art of necromancy. These fallen warlocks would pioneer many dark and terrible things, as this was their way. They took the corpses of those they slew and rose them up as the Nind. And the Nind served them as warriors and soldiers, and when death took one of those dark elves, and that elf had not prepared for his or her own resurrection, the Nind would stand as guardians of their Funeral Temples until their bones turned to dust.
The Nind are a fairly straight forward necromantic creation, and their method of creation is very old, and very old fashioned. The magics used stir the dark force of the Earth as well as drawing upon the seething energy of death to rise up a formidable creature that was once alive but served again in death. This combination allowed the Nind to retain something of itself, and as such most retain a fraction of their most accomplished skills and abilities. As most elves turned soldiers and mercenaries into Nind, the majority of undead retained martial skills, rather than say, pottery making.
The Nind are devious foes.
Playing Possum: The Nind are not above laying down on the ground to look like long dead bodies. Some more vicious ones are controlled enough to allow themselves to be touched and moved without responding. The ambush tactic involves staking out a site where people will come and rest for a night. The undead are overlooked until they stand up later, inside magic wards and perimeters, and start makng the gutteral wolf noises and stabbing with stolen weapons and ripping at the faces and throats of their sleeping victims.
Swarming: Nind in numbers will rush anything that threatens them. This is intended to overrun an enemy and tear through their defenses. The Nind augment this ability by carrying things that double as shields, or one shot improvised weapons, such as carrying rocks and large pieces of wood to throw as projectile attacks. Even if a warrior isn't knocked down, he is still going to be stunned by stopping a 20 boulder with his shield, or face a hail of such stones. These bands of Nind typically collect stones the right shape and size for throwing, and can with enough time, flatten a man in a suit of armor.
Concealment: being skeletons and making no organic noises and having no need to twitch or move, the Nind are remarkabley good at being quiet and hiding. They will hide in unexpected places, waiting for foes to pass them before they lunge out with a spear, or a rusty blade to rip through exposed flesh.