Mer-People (Mermaids and Mermen) are Water-Folk who live primarily beneath the sea. Mermaids are the guardians and avengers of women. They can predict storms and future events. Some can even grant wishes. They are great teachers of wisdom and knowledge.
Water spirits can replenish our energy. They refresh and renew our spirits. Undines are usually female. The Undines work to awaken our deepest emotions. They stimulate our compassion and intuition. Just like guardian angels, each of us has an undine to watch over our life.
Mermen are generally considered uglier and by far less kindly than mermaids. They have no interest in mankind, unlike mermaids who often try to seduce human males, and are known for starting huge storms and drowning ships in ire and revenge if a mermaid is hurt. However, "Benwell... describes the Scandinavian Merman or Havmand as a handsome creature with a green or black beard, living on cliffs and shore hills as well as in the sea, and says that he was regarded as a beneficent creature." (An Encyclopedia of Fairies by Katharine Briggs)
Some, Mermen though, would warn of danger and be helpful, or even bring young sailor men down beneath the sea with them, where the men would either drown or live in blissful happiness, "depending on their captor's attitude"
The British Isles too had their fair share of merfolk mythology. The Cornish knew mermaids as Merrymaids; the Irish knew them as Merrows or Muirruhgach and some sources write that they lived on dry land below the sea and had enchanted caps that allowed them to pass through the water without drowning, while the women were very beautiful the men had red noses, were piggy eyed, with green hair and teeth and a penchant for brandy.
There is a theory that during the suppression of pagan deities, the mermaid and other minor supernatural beings were not seen as a threat to the growth and popularity of Christian beliefs. Some writers even go so far as to believe that the Church actually believed in the mermaid mythology, and for two particular reasons; the first is that the mermaid served as a moral emblem of sin, the femme fatale label we know so well was nurtured with this form of thinking; and the second was the quality of evidence from contemporary and ancient authors on the existence of mermaids added to this 'belief' the Church found in mermaids. Mermaids are the symbols of feminism, beauty, sexuality and fertility.