MASSUM'AA't

MASSUM'AA't is a tribe living in the lower regions of the Yuulón Mountains. Very little is known about them, as they live secluded lives and are hard to find when they don't want to be. Therefore even their size and organisation is unknown. As far as we can tell, they're peaceful, there is no record of them ever entering in a conflict with other known nations. They're mostly self-sufficient, although again how they provide for all of their needs is unknown. 
They do, however, seek some plants from the flatlands, and since they were occupied by the Empire, a trade or exchange developed between MASSUM'AA't and the local people. 
The reason they're famous are Morraks that they give in exchange for the products they want. Morraks are a form of art, a type of fabric with intricate patterns woven into them. Looking at them can induce the viewers into states of ecstasy. It wasn't clear how they created that item and achieved such effect.
It is speculated that because they're apparently peaceful, and were secluded in the mountains for so long, nobody had a reason to attack them. And because they didn't need to fight - they've develop such high arts.
Some people went there to discover if they had more secrets and special arts, but they either didn't return or their remains were foound in the mountains, proving the tribe wasn't entirely peaceful.
When one king tried to enslave the artistis-traders who brought the Morraks to the markets - it turned out they either couldn't produce anything in enslavement, or the secrets of their craft were more precious to them than their lives, and they all eventurally perished. After that, the trading ceased for some time - until the king relented and send conciliatory gifts. Since then, whenever the MASSUM'AA't come to trade, a few hostages are being sent in their place. They're kept in caves in the mountains, never actually taken to the heart of their country or settlements.