Your Dexterity score increases by 1, and your Charisma score increases by 2.

Your sylvan ancestry has adapted your physiology to both the twilight realms and the depths of the ocean. 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 can’t discern color in darkness, only shades of gray.

As an action, you can magically assume the shape of a seal. Your seal form is as unique as your human form and cannot be changed. While in seal form, you follow the same rules as a druid using the Wild Shape class feature. In addition, when you change shape from seal to human form, you shed your seal skin and must keep it safe and secure. As long as you have your seal skin in your possession, you may use your shapechanging ability at will and may maintain your seal form indefinitely. Without your seal skin you may not use your shapechanging abilities until the skin is retrieved, you are the target of a greater restoration, heal, regenerate, or wish spell, or you regenerate the skin after a year and a day.

Even in human form, you are as at home in the water as you are on land. Swimming does not cost you extra movement. You can hold your breath for a number of minutes equal to your Constitution score and may double any proficiency bonus you are allowed on Athletics checks to swim.

You can speak, read, and write Common, plus either Aquan or Sylvan. You may also speak to and understand all species of marine mammals as though under the effects of a speak with  animal spell. Though they speak Common, selkie accents are influenced by their Aquan and Sylvan tongues, causing them to stand out among local communities.