The creatures will be attacking a building en masse, defeated by the rise of the sun. The three biggest qualifications are that they are:
A: Strictly nocturnal, aka afraid of/can't function/will die in sunlight. Preferably not humanoid. Can be purely physical or more spirit-like.
B: Nothing 'normal', like vampires, werewolves, demons, etc.
C: Scary as all hell.
It doesn't matter where in the world these nasties come from, I just need something that nightmares are made of. Something perhaps Eastern European, but that's not necessary.
search terms: different versions of "mythological monsters" combined with "creatures" "nocturnal" "legend" "folklore" "Eastern European" "Middle Eastern" "South American" and more parts of the world, "scary" and other synonyms.
If anyone has any thoughts I would love to hear them. Thank you!