Pixies (also Pixy, Pixi, Piskies and Pigsies as they are sometimes known in Cornwall) are mythical creatures of folklore, considered to be particularly concentrated in the areas around Devon  and Cornwall,  suggesting some Celtic origin for the belief and name.
They are usually depicted with pointed ears, and often wearing a green outfit and pointed hat. Sometimes their eyes are described as being pointed upwards at the temple ends. These, however, are Victorian Era conventions and not part of the older mythology.
Etymology and origin
The origin of the name pixie is uncertain. Some have claimed that it comes from the Swedish dialectal pyske meaning wee little fairy. Others, however, have disputed this, claiming that due to the Cornish origin of the piskie that the term is probably Celtic in origin, though no known Celtic ancestor of the word is known.
Pixie mythology seems to predate Christian presence in Britain. They were subsumed into what passed as Christianity with the explanation that they were the souls of children who had died un-baptized. By 1869 some were suggesting that the name pixie was a racial remnant of Pictic tribes who used to paint/tattoo their skin blue, an attribute often given to pixies. This suggestion is still met in contemporary writing, but there is no proven connection and the etymological connection is doubtful. Some 19th century researchers made more general claims about pixie origins, or have connected them with Puck, a mythological creature sometimes described as a fairy ; the name Puck is also of uncertain origin.
Until the advent of more modern fiction, pixie mythology was localized to Britain. Some have noted similarities to "northern fairies", Germanic and Scandinavian fae, , but pixies are distinguished from them by the myths and stories of Devon and Cornwall.
Before the mid 19th century, pixies and faires were taken seriously in much of Cornwall and Devon. Books devoted to the homely beliefs of the peasantry are filled with incidents of pixie manifestations. Some locales are named for the pixies associated with them. In Devon, near Challacombe, a group of rocks are named for the pixies said to dwell there. In some areas belief in pixies and fairies as real beings persists.
In the legends associated with Dartmoor, pixies (or piskeys) are said to disguise themselves as a bundle of rags to lure children into their play. The pixies of Dartmoor are fond of music and dancing. These pixies are said to be helpful to normal humans, sometimes helping needy widows and others with housework. The queen of the Cornish pixies is said to be Joan the Wad (torch), and considered to be good luck. In Devon, pixies are said to be "invisibly small, and harmless or friendly to man."
In some of the legends and historical accounts they are presented as having near human stature. For instance, a member of the Elford family in Tavistock, Devon, successfully hid from Cromwell’s troops in a pixie house.  Though the entrance has narrowed with time, the pixie house, a natural cavern on Sheep Tor, still is accessible.
At Buckland St. Mary, Somerset, pixies and fairies are said to have battled each other. Here the pixies were victorious and still visit the area, whilst the fairies are said to have left after their loss. 
By the early 19th century their contact with 'normal' humans had diminished. In Samuel Drew’s Cornwall  one finds the observation: "The age of pixies, like that of chivalry, is gone. There is, perhaps, at present hardly a house they are reputed to visit. Even the fields and lanes which they formerly frequented seem to be nearly forsaken. Their music is rarely heard."
Pixies are variously described in folklore and fiction.
Pixies are said to be uncommonly beautiful, though there are some called pixies who have distorted and strange appearances. One pixie is said to have some goat-like features. Another is said to be coltish in character.
They are often ill-clothed or naked.  In 1890, William Crossing noted a pixie's preference for bits of finery: "Indeed, a sort of weakness for finery exists among them, and a piece of ribbon appears to be … highly prized by them."  Lack of fashion sense has been taken by Rachael de Vienne, a modern fantasy writer, to mean that pixies generally go unclothed, though they are sensitive to human need for covering.  In de Vienne's book, the main character, a pixie child, delights in ribbons made from her father's shirt.
Some pixies are said to steal children or to lead travellers astray. This seems to be a cross-over from fairy mythology and not originally attached to pixies; in 1850, Thomas Keightley observed that much of Devon pixie mythology may have originated from fairy myth. Pixies are said to reward consideration and punish neglect on the part of larger humans, for which Keightley gives examples. By their presence they bring blessings to those who are fond of them.
Pixies are drawn to horses, riding them for pleasure and making tangled ringlets in the manes of those horses they ride. They are "great explorers familiar with the caves of the ocean, the hidden sources of the streams and the recesses of the land." 
Some find pixies to have a human origin or to "partake of human nature", in distinction to fairies whose mythology is traced to immaterial and malignant spirit forces. In some discussions pixies are presented as wingless, pygmy-like creatures, however this is probably a later accretion to the mythology.
One British scholar took pixie myth seriously enough to state his belief that "Pixies were evidently a smaller race, and, from the greater obscurity of the … tales about them, I believe them to have been an earlier race."