Midjourney V4 has gotten pretty good at ponies. Inspired by https://derpibooru.org/images/3023487.

Most of these Rainbow Dash results use the following prompt:
high quality picture, cartoon style, my little pony, my little pony 4th generation, cyan pegasus character, rainbow dash, wings, pony, equine, pegasus, mane color rainbow, tail color rainbow, iris color magenta, wings spread, pony stands on the ground with four hooves, walking and looking towards viewer, dramatic scene, determined expression, hard rim lighting --v 4