Pixie

A piixie is a small, bright blue mischief-maker. Gilderoy Lockhart brought a group of them to Hogwarts in Harry Potter's second year, and lost control of them. He attempted to round them up using the incantation "Peskipiksi pesternomi!" Whether this is an actual spell is unknown. In the movie, Hermione froze the pixies in midair with the Immobulus spell.

In Fantastic Beasts and Where to Find Them, pixies were given a rating of XX.