A Mermaid is a female aquatic Fae species.
Mermaids live in seas and oceans.
A mermaid is a legendary aquatic creature with the upper body of a female human and the tail of a fish. Mermaids appear in the folklore of many cultures worldwide, including the Near East, Europe, Africa and Asia. The first stories appeared in ancient Assyria, in which the goddess Atargatis transformed herself into a mermaid out of shame for accidentally killing her human lover. Mermaids are sometimes associated with perilous events such as floods, storms, shipwrecks and drownings. In other folk traditions (or sometimes within the same tradition), they can be benevolent or beneficent, bestowing boons or falling in love with humans. Mermaids are associated with the mythological Greek sirens as well as with sirenia, a biological order comprising dugongs and manatees. 
- 2.04 Mirror, Mirror (mentioned only)
- 2.07 Fae Gone Wild (mentioned only)
- 2.17 The Girl Who Fae'd With Fire (mentioned only)
- 3.04 Fae-de To Black (a costume)
- 3.11 Adventures in Fae-bysitting (mentioned only)
- 4.10 Waves
NEED INFO RE MERMAID SPECIES IN EPISODE 4.10