Sir John Rhys's Celtic Folklore: Welsh and Manx (1901) paints a rather more frightening picture of Halloween than many other folklore collections, especially these descriptions of evil creatures:

...all uncanny spirits and bogies are at liberty [on this] night... The Hwch tu gwta is at large on Allhallows’ Eve, and the Scottish Gaels have the name ‘Samhanach’ for any Allhallows’ demon, formed from the word Samhain, Allhallows.