Elsewhere in Europe, mumming and hobby horses were part of other yearly festivals. However, in the Celtic-speaking regions they were "particularly appropriate to a night upon which supernatural beings were said to be abroad and could be imitated or warded off by human wanderers". From at least the 18th century, "imitating malignant spirits" led to playing pranks in Ireland and the Scottish Highlands. Wearing costumes and playing pranks at Halloween spread to England in the 20th century. Traditionally, pranksters used hollowed out turnips or mangel wurzels often carved with grotesque faces as lanterns. By those who made them, the lanterns were variously said to represent the spirits, or were used to ward off evil spirits. They were common in parts of Ireland and the Scottish Highlands in the 19th century, as well as in Somerset (see Punkie Night). In the 20th century they spread to other parts of England and became generally known as jack-o'-lanterns.
The practice may have originated in a Celtic festival, held on 31 October–1 November, to mark the beginning of winter. It was called Samhain in Ireland, Scotland and the Isle of Man, and Calan Gaeaf in Wales, Cornwall and Brittany. The festival is believed to have pre-Christian roots. After the Christianization of Ireland in the 5th century, some of these customs may have been retained in the Christian observance of All Hallows' Eve in that region—which continued to be called Samhain/Calan Gaeaf—blending the traditions of their ancestors with Christian ones. It was seen as a liminal time, when the spirits or fairies (the Aos Sí), and the souls of the dead, could more easily come into our world. It was believed that the Aos Sí needed to be propitiated to ensure that the people and their livestock survived the winter.