Alp

The Alp is the German equivalent of the nightmare spirit (cognate with the Old English 'elf' in its original malefic sense). Medieval German belief held that an Alp was often a living person — especially a child born with a caul — whose spirit left its body at night. The Alp wore a hat (Tarnkappe) that gave it invisibility and power; if this hat could be stolen, the Alp could be identified and confronted.

Invisible in its attacks, but when seen it appears as a small figure, sometimes with red eyes. It might appear as a cat, butterfly, pig, or dog. Its defining attribute is a small hat. Predominantly appears as a crushing weight on the chest.

Could enter through any opening and sit on sleepers. Caused erotic dreams or terrifying nightmares. Could also attack cattle, sucking milk from cows. Long-term attacks caused wasting illness. If its hat was stolen, it could be seen and named.