Changing their form requires a minute of concentration. When in merfolk form, they lose the ability to wear footwear or leggings of any kind (including magical types). In order to accommodate their changing form most landwalkers tend to prefer fighting in armor with armored skirts instead of greaves. 

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

You are proficient with the tools of one branch of artistry.

Merfolk can breathe in running water without difficulty. In stagnant water, such as a swamp or a small pond, Merfolk can breathe for 10 + CON minutes at a time, after which they must either surface or take 1 level of exhaustion per minute.

+1 to Wisdom and +2 to Dexterity ability scores

All Merfolk have resistance to cold damage, even when they are out of the water.

Merfolk can speak and write Common and Aquan