RTF is a global modification that replaces all towns in the game.

This is actually something unclear – Arthes always rides a horned horse, which is strange. And in Skyrim, there's the bone horse Arvak, which has some kind of growth sticking out from the back of its head like a pterodactyl's, presumably because a horse's head without a mane doesn't look good.

But I think this is a reference to bicorns – a medieval meme, where a unicorn is the embodiment of good, and a bicorn is an evil horse. Lilith also appeared from the tales of minstrels, and some consider her a canon from the Old Testament, lol.