Generated with Stable Diffusion txt2img and refined over several generations with img2img. Various prompts over the course of generation, but typically:
princess luna wearing heavy armor, masterwork award winning, ethereal, light shafts, mlp, pony, intricate, detailed castle background, twilight
You should look into inpainting in addition to img2img. It allows much more detail if you’re only regenerating a small region, like the face, or the individual castle towers.