FEY
Merfolk are a sapient species of liminal fey that have well-built and attractive humanoid upper bodies and lower halves consisting of the tail and fins of a great fish or whale. Their hair and skin span a wide range of hues, with merpeople in a given region closely resembling each other.
Living beneath the sea, there are mermaids and mermen that are separated from the interference of the other land-based societies and as such have been free to establish their own civilization beneath the oceans, and there are merfolk that live in mountain lakes, rivers, and even swampy wetlands shared by the land walkers of the world.
Merfolk Traits
Size: Medium
Speed: 30 feet
As a Merfolk, you have these special traits.
Fey Ancestry. You have advantage on saving throws against being charmed, and magic can't put you to sleep. Your innate magic sustains you so that you suffer none of the frailty of old age, and you can't be aged magically.
Amphibious Capability. You can breathe both air and water. You swim speed is equal to your walking speed. Underwater combat does not impose any penalties or disadvantages on movement or weapon attacks. While underwater you have darkvision, you can see in dim light within 120 feet of you as if it were bright light, and in darkness as if it were dim light. You can't discern color in darkness, only shades of grey.
Slime Coating. A thin coating of slippery slime is produced by your skin to stay moist in order to breathe through their skin underwater and on land. You have advantage on saving throws to avoid being grappled or restrained and to end the Grappled and Restrained conditions.
Aquatic Attunement: You know Shape Water cantrip. Starting at 3rd level, you can cast the Create or Destroy Water spell with this trait. Starting at 5th level, you can cast the Rime's Binding Ice spell with this trait. You always have those spells prepared. You can cast them once without a spell slot, and you regain the ability to cast it in that way when you finish a Long Rest. You can also cast the spell 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 species).