Lorelei

Lorelei, known as undines to scholars, are water-dwellers, though they may also be found behind waterfalls, and atop riverbanks. They are especially known for their beauty (though some use magic to conceal horrid appearances) and their singing, which has enticed many a sailor or boatman. Occasionally, lorelei come to human settlements and take on partners, much like fee, orcs, or demons. The affairs tend to be unhappy ones, and cost the human partner their life or their sanity. To the lorelei, the cost is a shortened lifespan (but the gain, priests say, is their immortal soul). When they become 'human' in this way, lorelei retain some of their native traits, called watermarks - green hair, a greenish-pallid hue, and occasionally, scales or gills. Children born of such unions are also considered lorelei for game mechanic purposes.
Lorelei Traits: +1 CHA
Language: You can speak the Aquatic tongue. If born among humans with no other lorelei contact, select a human language instead.
Amphibious: You have a 30 foot Swim speed, and can breathe underwater as if affected by a 3rd level Waterbreathing spell of indefinite duration.
Beguiling: You know the Friends cantrip.
Strength of the Deep: You have advantage on WIS saving throws against magical effects.