These "tricky little blighters!" as quoted by Gilderoy Lockhart are truly one of the biggest trouble makers known in HP! Beware of not knowing how to defend yourself from them or you'll find yourself hanging from a chandelier like our friend Neville. If he would've known how to round them up by saying "Peskipiksi Pesternomi!" he would've been safely on the ground XD
Cornish Pixies have shrill voices with pointed faces, colored electric blue and about 8 inches high. In this image the Pixie has wings but in the book it states they don't have any wings.
What bothers them the most? you might wonder....well, try screaming!!