I personally love that idea don't do mermaids though. Make them able to speak but in a different dialect and make it so you have to find a way to communicate if you want to talk to them. You could even make them hostile towards you at first. And may…
How bout emplementing the eggs as the ability to have one as a pet. I know you can tame a stalker but why not add in say taking a bone shark egg and hatching it in an incubator or something then releasing it to the sea to be your pet. Also add in th…