Back to the ponies? Or in this case Kelpie. Tide is a male Kelpie residing in a saltwater river, among the small stretches of coral reef that grow along the bottom. He’s not outwardly violent or aggressive, but he does prefer his space and solitude. Like traditional Kelpies he is a carnivore (with sharp teeth and all )- and eats other ponies and creatures that drown in his river. Unlike traditional Kelpies however, he doesn’t make it a point to lure and drown them. The river he lives in is deep and rises with the oceanic tide, and enough food gets caught and drowned with it for him to feed off of.  
When in a stationary sitting or lying pose, his mane and tail act as a waterfall, simply spilling down his back and over his face. When he stands and becomes active, the water levitates and spins around him. His hide is a dark grey, and his mane/tail is tinted blue water. He has stems of coral growing off of his head and flank, but its dark like his hide.