Merfolk

Ability Score Increase: Your Dexterity increases by 2 Shape Changing: As an action, when on land, you can magically assume the bipedal humanoid shape similar to that of an elf, human, or half elf. Your humanoid form appears as your merfolk form mostly, but with legs in place of a tail and a walking speed of 30 feet. In this form you lose your swimming speed and follow normal swimming rules. In addition, when you change shape from a merfolk to a human form, you store your merfolk essence in the form of a trinket, usually a seashell necklace or other such item of nature, to keep it safe and secure. As long as you have this item in your possession, you may maintain your form indefinitely. Without this item, you cannot shape change. If you lose it as a human, you cannot return a merfolk shape until you are the target of a remove curse, greater restoration, heal, regeneration, or wish spell. Then you must craft a new trinket to shape change again.  Water Breathing: You can breathe air and water Siren Song: Merfolk are known for their beautiful songs. You have proficiency in the performance skill.  Age: Merfolk have a lifespan similar to humans, reaching maturity by their early teens and rarely living longer than a century.  Size: Merfolk come in a variety of lengths and weights, ranging from 5-7 feet in length, and from 100-300 Speed: Your base walking speed is 10 feet and you are always considered prone. You have a swimming speed of 35 feet.  Languages: You speak, read, and write Aquan as well as one other language (typically common). 

Arctic Merfolk

(Orca based) Ability Score Increase: Your Intelligence increases by 1 . Cold Adaptability: You are resistance to cold damage and have advantage on saves against the cold.  Keen Hearing: Arctic Merfolk have advantage on wisdom (perception) checks that rely on hearing.  Pack Tactics: You have advantage on attacks against a creature when underwater if at least one ally is within 5 feet.

Open-Ocean Merfolk

(Shark based) Ability Score Increase: Your Strength score increases by 1.  Fast Swimmers: Your base swim speed increases to 40.  Ocean Sense: You always know which direction is north, as well as how deep you are below sea level, and what direction the surface is.  Blood Frenzy: You gain +1 to attacks and damage against anyone who has taken Slashing or piercing damage and have advantage against tracking them for 24 hours or until they heal. 

Deep Merfolk

(octopus based) Ability Score Increase: Your Strength score increases by 1.  Darkvision: 60 feet Deep resistance: resistance to cold damage Light sensitivity: disadvantage on perception checks that rely on sight in bright light. Underwater Camouflage: You have advantage on Dexterity (Stealth) checks made while Underwater when using camouflage.  Tentacles: You can attempt to grapple up to 4 targets (dc 8+strength modifier). Your tentacles are occupied while grappling.  Ink Cloud: once per long rest you can create a 10 foot cloud of ink that extends all around you, obscuring the area for 1 minute. A significant currant can disperse the ink. After using this action, you can dash as a bonus action. 

Tropical Merfolk

(tropical fish based) Ability Score Increase: Your Charisma score increases by 1 Reef Sense: You have advantage on persuasion checks against aquatic animals and humanoids. You can cast "speak with animals" once per short rest.  Pack Tactics: You have advantage on attacks against a creature when underwater if at least one ally is within 5 feet.  Poison: You are immune to poison damage and the poisoned condition.. You also know the Poison spray cantrip.