Quoted By:
Just now. Based off a Crown of Thorns starfish. Poison/Water would make sense. Or some kind of Starmie variation/progression.
The series in which it is introduced should have a significant sea section, but with rocky atolls, vast seaweed thickets, and thundering seas among the archipelagos (so every type may be represented.) The name of the Pokemon should be Crown O' [insert name of sea.]
Its ability: Its water type moves will have STAB and not be resisted by the water type.
Not a game changer, but a bro for your run of this fictional pacific-island-themed map. Probably slow and defensible.