Kitsune are vulnerable to virtuous officials.
Evil spirits can be kept from harming Japanese actors by sprinkling the stage with salt.
Vampires are obsessive compulisve counters.
Werewolves need their clothes to change back to human form.
Fairies are vulnerable to iron, bread, church bells, clothing turned inside outside, and running water.
Rumpelstilskin and his ilk are vulnerable to their true names and seem to usually be forced to tell their victims that.
Etc. Even though -- especially though -- not all of the creatures suffer all of the vulnerabilities associated with their type.
I've got an idea that turns on their random nature. But looking at the starting outline, I realize -- gotta research first. 'cause which creatures I choose will determine a lot of the plot, and I need to know their vulnerabilites. Sometimes you can't just let it grow and determine what you need after.