Thunderhorses

I remember when I was small child, I got told that thunder is caused by Ukko (Ukko Ylijumala = Ukko Overgod,  god of the sky, weather, harvest and thunder) riding his rock sleigh on the sky. I got told this probably several times, because I remember it so well. With child's imagination I figured the sleigh must have been pulled by very strong creatures - and when I heard thunder, its power, I associated all that information with horses.
Thus I started to believe there were strong, black horses pulling the rock sleigh of Ukko. Later I started considering the horses might be running there on their own, also, sometimes - as a huge herd. Black and intimidating as a thunder.

I know they look mostly like friesians, but they are a bit bigger (although size is relative as they are otherworldly, mythical creatures for which shapeshifting is not unheard of). They are also very strong, and they can run in the air. Their breath is moist and usually cold like a strong wind. They are mostly black with dark eyes, but rare, unique eye colors like blue and gold do appear sometimes. When they run, excited, their hooves cause banging noises as they slam against the air with pressure. When they do this enough, clouds form under their legs, and eventually thunderbolts start to occur.

These five are the thunder horses I've characterized in my head over the years. Thunder was the first (as a child I had a horse figurine I imagined being Thunder). Others came eventually, Coldborn being the newest.

Their names are in the sheet in both English and Finnish, both versions are in usage.

Thunder is the leading male of the herd, and even if I've introduces only these five individuals, the size of the whole herd is somewhere around 100 horses.

While any thunderhorse could basically shapeshift and take human form, most of them don't do it. In the end they are primary equines and content with it. Thunder is old as sky, so he have had time and eventually also a need to get used to the human shape. Coldborn is an exception, since she was originally human: she died by thunderbolt hitting her, and was reborn as a thunderhorse. She is comfortable with her human form, and while Thunder is plain and casual with what he is used to wear as a human, Coldborn has more eye for the fashion.

...yeah I know this might seem like I've stuck with black horses (or black characters overall) lately, with similar designs and such. But these aren't quite even characters to me, they are something I've imagined from when I was child. And Viscoum was a creature I saw in my dreams. Gee, my unconscious mind is the one we should blame ;v;