Being aquatic creatures, merfolk are excellent swimmers. Being able to reach speeds of 60 feet.

When wearing amour not adapted for water, their speed becomes 50 feet.

From dwelling in the depths of the ocean where the light cannot reach, merfolk have darkvision of 100ft.

Merfolk take refuge in the cold shadows of the sea and feel at home in the chilling waters. You have a resistance to cold damage.

Being a creature of the sea, merfolk are sensitive to heat and fire. You have a vulnerability to fire. 

Having gils and scales means merfolk need a suffient water source to survive. They can last without water for 6 hours, but that can lower to as much as 1 hour depending on the climate.

Mermaids ae known for their melodic voice, drawing in those who are sung to. You can cast Charm once per lost rest.

In the dark shadows, a merfolk's true form shows itself. They become hideous, thin creatures, no longer the beautiful beings they're believed to be. Their scales become frayed and dark, and their face change from human to the likeness of deep-sea fish.

Those who see them like this no longer fall for the merfolk's alluring demeanour, instead growing detested of the monster before them.

When in this form, you have -10 charisma. This doesn't affect intimidation.

You have +2 charisma and +1 dexterity.

You possess innate survival instincts and basic emotions rooted in your fishy ancestry. These primal urges impact your behaviour. 
You are proficient in survival.