“Nightwalker” is a pretty good name for night-aspected earth ponies. I might have found it hard to come up with something distinctive, but that really works.

@Background Pony #48E2  
I’m pretty sure the (language-corrected) term “night guard” predates the actual Goths, since it’s just a different way of saying “night watchman”, to differentiate from the city/private guard who patrolled in the daylight.

I have to say, I really like the term “saberhorn.” It just has a nice flow to it. SABERHORN!

For the night is dark and full of terrors… I guess.

Night Guard rivals the Dark Brotherhood in terms of organization names that sound like they were thought up by high school goths.

@Background Pony #7638  
There are also Crystal Pegasi, so it seems like the show is already taking the route of having different races of the Three Tribes; I think it’s most likely that the Crystal Ponies were modified en masse by the Crystal Heart at some time in the ancient past (possibly before the founding of Equestria, since their overall Ancient Grome aesthetic seems intended to convey ancientness), and there just happened to be a majority of Earth Ponies around at the time. My headcanon until the show contradicts it is that there was a minor Earth Pony kingdom that either found or constructed the Crystal Heart as a way to survive the nationwide blizzard caused by the Windigo, and since it required the cooperation of everypony in the kingdom to make it work, they managed to work out their own version of the Magic Of Friendship that the three leaders discovered on the first Hearth’s Warming Day.

One thousand years ago, superstition and the magic ruled.  
It was a time of darkness. It was a world of fear. It was the age of bat ponies.  
Stone by day, warriors by night. We were betrayed by the Princess we had sworn to protect, frozen in stone by a magic spell for a thousand years.  
Now, here in Manehattan…the spell is broken. And we live again!  
We are defenders of the night.  
We are BAT PONIES!

This is cool.
 
Curious, where do Crystal ponies fit into your headcanon then? A specially adapted form of Earth pony, something Sombra or something a device or magical power like the Crystal Heart created or what?