There is just something magical about imagining what life is like down in the depths of the vast ocean. Some areas of which, mere humans can only dream of exploring...
When illustrating merfolk, I love giving them gill-like fins in place of ears and adorning them in shells and strands of pearls. This one has a rather simple tail, but if making the tail the focus, you could be as creative as you want with the vein design and the number of fins drawn.
Other ideas for inclusion in merfolk illustrations: Bejewelled crowns, intricate shell hairpieces, fallen human treasures, webbed fingers, blue-green complexion, sea-anenome hair, starfish headpiece, scales extending over the entire body...the creative options are endless!
This is my favourite mermaid illustration by Kei Acedera from Imaginism Studios:
I just love the cute cartoon style, the minimal colour palette and use of under-the-sea features.