Ancient Unicorn

Unicorns born of wild, untamed magic in various areas across Equestria. 
Where other ponies shape their ecosystem to their will, it is the duty of the Ancients to instead work beside it. Creatures of serenity and acceptance, their long lives are most often spent in solitude carrying out their tasks. The spontaneous, erratic minds of the other pony races seem entirely alien to them, causing them to doubt what they do not know.
Their life is tied to a tree. Though the species of tree may vary, any blessed with its own magic can bear a foal. However, such a tree is extremely rare. The unicorn shall live for as many years as their tree stands tall, should it die the unicorn's fate shall be mirrored. However if the unicorn shall perish, the tree's life shall be unaffected. 
Rumours of their existance have been passed down in Pony lore, tales of voices whispering in the forest and unseen equines guiding lost travellers to safety or doom within the forest boundaries. Zebra's one of the few holding any tales of truth with the Ancient Unicorns, communication betwen the species held out only when needed. 
Ancients born of magic feed on magic, acting almost as a containment for the wild magic. They grow to a height nearly on par with that of that of the Alicorn princesses, but with a distinctly slender frame. Their horns are often twisted or bent, as if to mimic the braches of the trees from which they are born. The Ancient Unicorn's tail resembles that of an ox, and tufts of fur often cover portions of their bodies.