I'm a sucker for using commonly known creatures in my settings partially because I think they're super fun but also because they give me some building blocks to work on with to make something more personalized out of them to fit my settings better!
For example with vampires I have explained their sensitivity to garlic and sunlight with a chronic migraine, as funnily both are very common migraine triggers to people, including me! I also added that vampire children start out functioning like humans in order to ensure higher percentage of survival, and only as they start maturing they slowly grow a distaste to human food (many stop tasting things outside of blood) and start showing signs of slowly developing chronic migraine. They also can't fly on their own, but they know how to make cloaks that help you fly, to sort of acknowledge the myth of vampires flying or turning into bats (in which capes usually serve as a visual way to morph the shape from human to a bat).
As for dragons I have several takes on them depending on the worldsetting, but my favourite is probably Enhyria where dragons become mad if they taste enough human blood! Enhyria is very fairy tale based and while I love dragons and consider them usually as "the good guys" pretty much I wanted to somehow acknowledge the Evil Dragon Beast trope and thought becoming mad from human blood would serve as an interesting take in context of my own stories. They can also communicate through a more abstract sort of mind communication so even if you don't speak the same language the message will get across! It doesn't work as a normal dialogue would but instead through several mental images and feelings the dragons are experts at deciphering.