Homebrew
You can see in dim light within 60 feet of you as if it were bright light and in darkness as if it were dim light. You discern colors in that darkness only as shades of gray.
You can breathe air and water.
You naturally have proficiency with tridents, as well you can make a bonus action to make a second attack with tridents.
You can cast fog cloud and shape water with this trait. When you cast fog cloud only you and other tritonkin can see within the fog. Starting at 5th level, you can also cast the water walk spell with it. Once you cast any of these spells with this trait, you can’t cast that spell with it again until you finish a long rest. You can also cast these spells using any spell slots you have of the appropriate level.
Intelligence, Wisdom, or Charisma is your spellcasting ability for these spells when you cast them with this trait (choose when you select this race).
You can communicate simple ideas to any Beast, Elemental, or Monstrosity that has a swimming speed. It can understand your words, though you have no special ability to understand it in return.
Adapted to the frigid ocean depths, you have resistance to cold damage.