Näcken

Näcken, also spelled neck, nicor, nixie or nokken, is a shapeshifting water sprite. It first appears in "A Fistful of Warlocks".

In the series
Näcken are huge, foul-smelling water dwellers, capable of assuming the shape of a horse. One of them, Having lost a bet with Anastasia Luccio, is bound to assist her in the chase of Heinrich Kemmler.

Trivia
Näcken is the swedish name for male water spirits, invariably male, who often entice women and children to drown in lakes or streams by playing the violin. Similar faerie are present in North Europe, from the Germany to Scandinavia and the UK.