seeing as i believe that most if not all mythical creatures are real in one form or another

if mermaids did exsist, would we be looking for creatures like Ariel, the girls from H2O, ect
or would we be looking for something darker and far more beastly like the mermaids in the black lake of Hogworts, she creature, peter pan and POTC on stranger tides.

which mermaid does your mermaid person fall in league with?