I have not had time to play in a campaign in years. I write because I am a writer and games are my milieu. Eventually my goal is to be published and make some regular income...
The World of Greyhawk has sea sprites, which I gave wings like flying fish fins. And I too have aquatic thri-kreen, inspired by the aquatic nymph stage of some insects.
Wow! I just stumbled upon this thread and it is chock full of gaming goodness That Thalassan aquatic elf twist is pretty ingenious.
So, the "Spell & Crossbones" link in my sig may be of interest to those of you into pirates and such. While it has a 5e bent, much of it is edition neutral, and I've even outlined a reinterpretation of the Abyss as horrific watery demonic depths. Oh, and flumphs are psionic jellyfish that appear at night to warn of doom from undersea aberrations!