Tale of The One Who Watches

This is an old Changeling tale. Noling is quite sure how old, but they all agree that it is so.

There was once a changeling. They lived a normal life, as a guard. One day, however, they saw a pony, fearlessly approaching the hive.
"Who are you?" The changeling hissed at them.
"Relax, my friend. All I would like is a lesson." The pony replied.
"A... Lesson?" The changeling hesitantly asked. After all, here was a pony, asking for help from a changeling of all things!
"Yes. I would like to see if I can learn changeling shapeshifting."
At this, the changeling laughed and laughed. A pony, hoping to learn an ability of the changelings? Ridiculous!
Seeing this display, the pony only smiled. "I may have more success than you think." They stated.
Their curiosity peaked now, the changeling agreed. The two sat down, and began the lesson, the changeling using methods taught to them as a nymph.
Amazingly, the pony did it! In a weak burst of blue flames, the pony changed their appearance completely! The changeling was astounded. They had thought it was a joke! They didn't think this pony would even be capable of this!
The pony thanked them, and walked away, being too far before the changeling finally registered this was a possible threat. Since they couldn't go after the pony themselves, they told the whole hive of the pony that learnt their power in a single day. The hive then told their children, who told their children, who told their children, this strange tale. At this point, it had stopped being a warning, and started being folklore.

Exactly fifty years later, a pony walked up to the hive, calling out to the changeling on duty,
"Hello there!"
The changeling shrieked in shock, before picking up their dropped weapon and hissing at them.
"What do you want? Who are you?"
"Oh, hello deja vu. How are you doing?" The pony muttered to themself. "I merely wanted to see how you were doing! My my, it has been a while, hasn't it?"
The changeling hissed in confusion, understandably. Why was this pony talking like they were seeing an old friend?
Said pony suddenly gasped, hitting themself in the face with a hoof. "Of course, I'm an idiot. You have no idea who I am, do you?" The pony called.
The changeling warily shook their head.
"Of course. Well, I merely wanted to see what was going on. I'll leave for now!" And with that, the pony walked away.

From that day onward, every fifty years, the same pony would show up at the west side of the hive, at the exact same place. It is the only part of the hive that has never been renovated, for fear that the pony may not be able to find the location, and may give up and never come back. The pony's method of arrival may change, be it walking, teleporting, or their own changeling fire, but it was always the same pony. Noling knows what they look like, as any guard somehow forgot the pony's appearance once said pony was gone. However, they have never failed to appear, no matter what. Even if the day is a dark one, of storms and hail, the pony would still appear, the only difference being that they would be dressed in a black cloak. Noling is even sure what tribe of pony they are. Most agree they probably have a horn, but horned pegasi, alicorns, and the like do exist.