Pixies are magical creatures native from Earth. They have multiple looks in the English lore, but in the TV Show, they appear to be human with the exception of pointy years.
They are able to live more than 500 years old , are known trickester and love riddles and puzzles.
Brakebills and Battle Magic
For a long time Brakebills University for Magical Pedagogy had classes on Battle Magic. The main teacher being a pixie named Neeny Bigby. In 1979, the board of the school decided that learning Battle Magic was too dangerous for students as they could use it for ill intent or to battle each other. They decided to remove the subject from the teachable subject of the school 
Neeny Bigby warned the board that there will be a day where students will need to defend themselves and have Battle Magic and their lack of knowledge on the subject will prove a great problem. She then disappeared never to be heard of.
In Hotel Spa Potions, they manage to find her as she had left clues of her whereabouts in different books. This lead them to 219 Summerset in Rhode Island where she lived. She then gloated that their presence proved the board that she was right about the subject teaching. She will then provide Alice Quinn with the Rhinemann Ultra