I am definitely part of the group Kisota mentions - my form would probably fit better under a mythic umbrella (I do love the merfolk community), but because the experience of shifts is central I feel therian circles are more appropriate.
I think its always tempting to identify with monstrous characters because of an analogous experience of 'otherness' - but when it comes down to it my BIG SCARY urges include things like catch fish and maybe I'm poisonous ... ¯\_(ツ)_/¯ . Characters like Abe Sapien and the creature from the Shape of Water all resonate for me, but maybe my theriotype is just Doug Jones.
On a spiritual note I've found it useful to force a more predatory/scary/monster-like shift when doing some astral work. The shift focus goes from swimming/fins/gills to claws and teeth - which are definitely there - but perhaps not as exaggerated as I make them for the sake of a working.
"One does not meet oneself until one catches the recollection from an eye other than human" - Loren Eiseley