Huldrefólk

The Huldrefólk (singular: Hulder) are creatures living in the underground city in the abandoned mines below Miner's Mountain. The Huldrefólk find lost things and store them in a turf house on the surface, which they call Library of Lost Things. The Nattmara are their natural enemies. Long ago, they lived in peace with humans, but in the present they hide away from them and defend themselves if disturbed.

Notable Huldrefólk

 * Librarian King - the leader
 * Echo - a child from the royal family
 * Obscuren - the Librarian King's assistant

Appearance
Adult Huldrefólk are tall and strong, with long limbs and necks and sharp ears. Their skin changes color to match their surroundings and help them hide. It is debated if they have tails and mentioning it is considered rude by the Huldrefólk and the Huldrefólk hide their supposed tails under clothing, like skirts or push their backs towards walls. Stories say that they eat those who ask about their tails. The king is the tallest Huldrefólk and has a black mane.

Culture
The Nattmara are their enemies, as both use the night and dark, but the Nattmara use it to attack while the Huldrefólk use it to hide.

When their underground city is visited by unexpected guests, they protect it, fighting using spears and push their enemies into magma.

While Huldrefólk understand the language used by humans, most of them usually reply in single words rather than sentences, with the Librarian King and Obscuren being exceptions as they came into contacts with human language more, especially the former, who had spent years on the surface collecting lost things and stories.

The royal family of Huldrefólk are defenders of their city.

The Huldrefólk use pumice rafts as a means of transportation on underground rivers.

The Huldrefólk use runes to write.

Trivia

 * The Nattmara cannot sense magic or sleep or influence anyone in the Huldrefólk's domain.
 * Aren of Arendelle helped the Huldrefólk hide their tails.
 * Some Huldrefólk, Obscuren's family, use 'Till we see you again.' as a farewell.
 * Idunna read about the Huldrefolk in Dangerous Secrets.