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An alp is a nightmare creature originating in German folklore.
Not to be mistaken with the similarly named Alp-luachra, the alp is sometimes likened to a vampire, but its behavior is more like that of the incubus. It is unique from both of these creatures in that it wears a magic hat called a Tarnkappe, from which it draws its powers. The word "alp" is a variation on the word "elf". It is also known by the following names: trud, mare, mart, mahr, schrat, and walrider. Many variations of the creature exist in surrounding European areas, such as the Druden and Schratteli.
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