O mighty LJ hivemind
I'm working on a list of references to sleep/dreams/memories, creatures who can affect those, and/or just general starting point references for them.
Al Basti - tormenting female night demon in Turkish folklore (Anatolia, Turkmenistan). (thanks, miz_placed!)
Alp - nightmare creature originating from Teutonic or German folklore. (thanks, miz_placed!)
Ancestors/friendly spirits can appear in dreams (thanks, keerawa)
Asclepius used to give dreams that could be interpreted for remedies for illness
Australian aborigines dreaming/dreamtime
Batibat - Filipino, Illocano, demon that sits on sleeping person's chest. (thanks, miz_placed)
Baku: good Japanese creature (lion's head, tiger's feet and a horse's body) that eats the evil out of nightmares.
Baron Samedi, the voodoo god of the crossroads, can show up in dreams
Dream of the Endless (Neil Gaiman's Sandman series, thanks lferion!)
Dream/underworld connection from Gilgamesh (lferion again)
dream walking (Native American black magic; thanks alexandralynch)
Encephalitis lethargica, aka sleeping sickness (What? Parasites should count, right?)
Gods whose priests interpreted dreams: several, including Nanshe, Hathor, Gestianna (Dumuzi's sister)
Golem: the Kabbalistic formulae for creating a golem were communicated in dreams
Incubus or succubus
Joseph's prophetic dreams in the Bible (thanks, Devo!)
Karakura - Turkish (East Anatolia) folklore, a tormenting masculine night-demon, or nightmare. (thanks, miz_placed)
Lucid dreaming (thanks, KickA!)
Mara, A goblin from Scandinavian folklore who seizes men in their beds and takes away all speech and motion.
Munin, Odin's raven Memory
Night mares
Nocnitsa, night-hag of Russian, Polish, Serbian, and Slovak folklore. She torments children at night. In some regions, the mothers place a knife in the cradle or draw a circle around it with a knife. Hiding an ax or a doll under the floor beneath the cradle also prevents her from getting at the child (possible based on the belief that supernatural beings cannot touch iron). Other names for the hag include kriksy and plaksy. Her Bulgarian equivalent is the gorska makva, a hideous wood-hag.
Nursery rhyme: "Winken, Blinken, and Nod" (thanks lferion!)
Oneroi: (Greek) The Oneiroi are the personified deities of specific types of dreams such as nightmares, sexual dreams, etc. They were thought to dwell on the shores of the Ocean in the extreme west. True dreams issue from a gate of horn, while deceptive dreams issue from a gate of ivory. (Morpheus and his sons, among others)
Psychology: Freud called dreams the royal road to the unconscious and Jung saw them as where we meet archetypes. (thanks, Devo!)
Ragshiel: Angel of dreams.
Rip van Winkle's long nap after watching the fae/dwarves bowling
Shamanic dream trances (I don't know if they can pull people in, but it's on the list)
Sleeping Beauty of course
Tavara or Davara - Trabzon folklore (city in Black Sea region of Turkey), a tormenting night-demon, or nightmare. (miz_placed again)
Witches: flying ointments frequently gave flying dreams, seduced in dreams, could travel in or send bad dreams.
Vampires. The old ones in Forever Knight, at least, could give/remove/rework memories
Zakar: Babylonian god of dreams, which were messages from the gods
I'm certain I've missed plenty. This is one of those where as soon as I post I'll probably remember four more, but what've y'all got? I'll update the list in the morning, and thank you!
ETA: 04/05/08 added the first five commenters' suggestions, plus a few more from Encyclopedia Mythica.
Al Basti - tormenting female night demon in Turkish folklore (Anatolia, Turkmenistan). (thanks, miz_placed!)
Alp - nightmare creature originating from Teutonic or German folklore. (thanks, miz_placed!)
Ancestors/friendly spirits can appear in dreams (thanks, keerawa)
Asclepius used to give dreams that could be interpreted for remedies for illness
Australian aborigines dreaming/dreamtime
Batibat - Filipino, Illocano, demon that sits on sleeping person's chest. (thanks, miz_placed)
Baku: good Japanese creature (lion's head, tiger's feet and a horse's body) that eats the evil out of nightmares.
Baron Samedi, the voodoo god of the crossroads, can show up in dreams
Dream of the Endless (Neil Gaiman's Sandman series, thanks lferion!)
Dream/underworld connection from Gilgamesh (lferion again)
dream walking (Native American black magic; thanks alexandralynch)
Encephalitis lethargica, aka sleeping sickness (What? Parasites should count, right?)
Gods whose priests interpreted dreams: several, including Nanshe, Hathor, Gestianna (Dumuzi's sister)
Golem: the Kabbalistic formulae for creating a golem were communicated in dreams
Incubus or succubus
Joseph's prophetic dreams in the Bible (thanks, Devo!)
Karakura - Turkish (East Anatolia) folklore, a tormenting masculine night-demon, or nightmare. (thanks, miz_placed)
Lucid dreaming (thanks, KickA!)
Mara, A goblin from Scandinavian folklore who seizes men in their beds and takes away all speech and motion.
Munin, Odin's raven Memory
Night mares
Nocnitsa, night-hag of Russian, Polish, Serbian, and Slovak folklore. She torments children at night. In some regions, the mothers place a knife in the cradle or draw a circle around it with a knife. Hiding an ax or a doll under the floor beneath the cradle also prevents her from getting at the child (possible based on the belief that supernatural beings cannot touch iron). Other names for the hag include kriksy and plaksy. Her Bulgarian equivalent is the gorska makva, a hideous wood-hag.
Nursery rhyme: "Winken, Blinken, and Nod" (thanks lferion!)
Oneroi: (Greek) The Oneiroi are the personified deities of specific types of dreams such as nightmares, sexual dreams, etc. They were thought to dwell on the shores of the Ocean in the extreme west. True dreams issue from a gate of horn, while deceptive dreams issue from a gate of ivory. (Morpheus and his sons, among others)
Psychology: Freud called dreams the royal road to the unconscious and Jung saw them as where we meet archetypes. (thanks, Devo!)
Ragshiel: Angel of dreams.
Rip van Winkle's long nap after watching the fae/dwarves bowling
Shamanic dream trances (I don't know if they can pull people in, but it's on the list)
Sleeping Beauty of course
Tavara or Davara - Trabzon folklore (city in Black Sea region of Turkey), a tormenting night-demon, or nightmare. (miz_placed again)
Witches: flying ointments frequently gave flying dreams, seduced in dreams, could travel in or send bad dreams.
Vampires. The old ones in Forever Knight, at least, could give/remove/rework memories
Zakar: Babylonian god of dreams, which were messages from the gods
I'm certain I've missed plenty. This is one of those where as soon as I post I'll probably remember four more, but what've y'all got? I'll update the list in the morning, and thank you!
ETA: 04/05/08 added the first five commenters' suggestions, plus a few more from Encyclopedia Mythica.