While nymphs, in general, are not inherently malicious, they do have their darker sides. The xana, for instance, replaces human babies with their own. Some tales talk of darker colored xanas, who crawl through keyholes and steal belongings or bite the people living inside.
Some tales mention enchanted xanas who need help to release themselves of the spells and curses cast on them. After being unbound by the curses, the xana repays with gold and silver that it has either stolen, or found, before returning to its source of water.
- Should a xanino, a baby xana, be exchanged for a human infant, it will grow up within a matter of months.
- Asturians have a method of telling if the child has been changed, which is placing eggshells near fire to make the young xanino exclaim his true nature, despite his young age.