You might want to check this page out: List of legendary creatures by type
It gets kind of fuzzy when you're trying to define exactly what counts as a "legendary creature" though. Do creatures unique to modern sci-fi/fantasy literature, TV, or RPGs count? What about those invented by writers from the 1800s? How about the "fearsome critters" of North American folklore? Medieval literature also had plenty of books with more types of weird demons than you can shake a stick at.
For the older creatures, though, you can definitely discern clear archetypes which are often mixed together in various ways. Blood-drinkers, animal shapeshifters, literal sexual predators, and child-eating bogeys are pretty much universal. These may be mixed together in almost any combination. Lilith and her ilk get extra points for having all four.
Let's not forget water-dwelling predators, which can be found in almost any non-desert culture and typically have one or more of the above qualities. It is telling that the "associated with water" section is by far the largest on the Wikipedia page.
Giant humanoids, restless dead, witches with vaguely-defined magical powers, creatures that are an omen of death, creatures that can kill you by looking at you, and mischievous spirits that may be either helpful or harmful depending on how they are treated are extremely common as well. Cultures that valued either wisdom or piousness (both East and West) often had monsters that represented a more subtle threat than the ones who would simply eat you, like tengu or demons. The idea of automatons made by magic or technology is also more common in ancient stories than a modern reader might expect.
Then you have the weird ones, like the dream eating Baku, the mind-reading Satori, the Rokurokubi, a woman with a floating head... actually 90% of Japanese monsters can probably be thought of as 'weird' to Western audiences, though no weirder than the aforementioned medieval demons from the west (like wheels covered in legs...seriously). And of course, creatures that are just mash-ups of other creatures are fairly typical, especially among Mediterranean cultures. We might be accustomed to Greek creatures like the Chimera and the Hydra, but from a standpoint of common mythological archetypes they are no less mold-breaking than the wackiest of Japanese yokai.
Some archetypes may be more common in certain cultures than others - for instance, Celtic culture tended to have a lot of unpredictable but sometimes-benevolent fae, while most Greek monsters are Always Chaotic Evil. Certain concepts are also culture-specific and may spawn many unique monsters; for instance the idea of mundane creatures or inanimate objects 'advancing' into magical creatures or animated spirits (kitsune, carp -> dragons, tsukumogami) when they get old enough is a common idea in Japan, while Western monsters are typically born monstrous (except when they are ghosts).
Keep in mind that many archetypes may be blended unpredictably, even within the same "creature". For example, while modern culture tends to separate vampires and werewolves, many cultures view bloodsucking and animal shapeshifting typical habits of the same creature.
There are also some weaknesses shared by many different monsters - sunlight, silver, an inability to cross running water, obsessive-compulsive counting, and occasionally salt are shared by several members of the nebulous werewolf/vampire/witch family and their relatives, depending on the particular legend. Iron is a common weakness among various fae. A lot of spirits and demons are susceptible to certain incantations, and wherever Christianity touched you'll find stories of monsters that are repelled by faith or holy symbols. Yokai can sometimes be outsmarted by separating them from the source of their power (the kitsune's ball, the kappa's water).
In fact, the very idea of a mythical 'bestiary' might not be the best way of going about classifying monsters in a "fantasy kitchen sink" setting, given their tendency to blur together. Classifying the archetypes themselves and making each individual creature an unpredictable blend of said archetypes might be a better idea. But that's just my two cents.
