kurizeria

I never finished her full front/back reference, but I have Mira who is sea dragon inspired albeit very simplified:

I had a second one who was more jellyfish inspired so her "horns" were instead droopy and more like the oral arms of a jellyfish, but I don't have her file anymore since it was a SAI file and I lost all of those. I have to redraw her (and her adoptive father) but I'm so lazy AAAA I do still have this rough concept that survived though! Her final look was pretty different.

As for tips, I guess it also depends on how much you want your elf to blend in with the crowd vs giving them a more individualistic appearance? The vast majority of elves of the same species tend to have the same fashion going on, save for a few outliers OR those from different factions (Bloodmoon elves, or the Dawnbringers from the mobile game).

In a lot of the designs, sometimes adding extra detail to them can be as easy as adding a few curved lines to the clothes, or a subtle/repeating pattern to make an otherwise simple design look a bit more intricate (such as the subtle pattern on the red of arc 1 Callum's shirt). If you aren't sure about what pattern could be nice, maybe looking at things like the details on more intricate pottery/vases, or the patterns on embroidered wall carpets could help?

Unfortunately since they aren't present in any Tales of Xadia campaign, there isn't much for Tidebound elves to really reference from outside of the old male & female concept arts, Akiyu, and Finnegrin. The latter has that outlier kind of design since he doesn't swim as much as others and is supposed to look like a sea captain though. But even between those select designs, we see a lot more variety in their horns and fins than we've seen in other kinds of elves so far! So I guess if anything, it might be worth looking at real fish for inspiration? Especially tropical fish, many of them have some interesting striped or spotted patterns and some pretty colour combinations! You might be able to apply them to your character or their outfit(s).