I am unsure about what diety I should pick for my character, as no one really sticks out like a must worship for a deep sea merfolk. I was kinda thinking about a god of heat or magma, as their home would be off the continental shelf, especially around faultlines, hotspots and smokestacks which could both be farmed for smaller critters feasting on the nutritious soup of hot, chemical rich water, and provide shelter from larger, predatory sea creatures inhabiting the depths. Which is incidentally also why I removed the elemental resistance to fire, as it doesn't really emulate a weakness to drying out as much as one for flammability, and fish, even while on land aren't that flammable! I am keeping the elemental weakness to lightning though, as they are bound to fry the biochemistry responsible for their bioluminescent orbs on their head, as well as along their tail.