Another one of those old seapony requests I offered on deviantart last year. This one was for a user called YulizieLove, and this is their OC DJ Vanessa Love, an alicorn turned seapony with a sturgeon fish tail.
 
I figured out a way I like to differentiate the different pony races. I know in the movie the unicorns/alicorns keep their horns normal, but I chose a different way (as again, like i said, these were before the movie came out). For unicorns, they get that angler fish-like dangler in place of their horns. The light-up orb on the end is the same color as the unicorn’s eyes and lights up/glows when they do magic. Pegasi get the extra back fins in place of where there wings would be that I purposely make resemble the fish’s fins. Earth ponies get neither. Alicorns, like Vanessa here or Luna in another picture I have on here, get the dangler and the extra back fins (dorsal fins aren’t the same; earth pony seaponies can have those depending on the fish). I always put cutie marks (if applicable) up on the shoulders of the seaponies. I didn’t like it trying to be on their hindquarters when they were fish and didn’t have any, and I’m not a big fan of how they were put on fins in the movie, but that’s my design choice.