You have a mermaid tail that is about the same length as human legs. 

Thanks to your Merling heritage, you have superior vision in dark and dim conditions. 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; Yes this does work underwater.

Being from the water, you have an attack bonus when attacking from the water. 

While staying near water for a rest you have an option to go into the water, if you do go into the water, whether it'd be a in a pond, river, lake or ocean. All of your needs will be met and your rest will go up a little.

Being a Merling you might have human legs, but it doesn't mean your good on land.