NOTE: Many of the humanoid creatures below exist in real-world lore as well. For our purposes, we are taking liberties with facts to tell our story. None of the information below should be considered representative of real world history and culture.
Vampires generally meet the following three criteria:
They are no longer alive, but remain conscious.
They require outside sustenance to survive.
They inherited at least one vulnerability from a sire.
This vague collection is intentionally non-specific. The most commonly considered vampires are the ones who feed on blood and are vulnerable to daylight. Based on the power of belief, some vampires are vulnerable to holy water and religious paraphernalia.
Like any species, blood sucking vampires have cousins and distant relatives who feed off many different things after their death.
Likewise, the vulnerabilities vary. Sunlight is the most common vulnerability, but others include silver, moving water, and wood.
In general, a vampire can always be defeated by chopping off their head, but most vampires these days are relatively harmless. If properly managed, a vampire can go their entire existence without killing anyone - usually.
In the 1200's-1600's, the Sentinels were at their peak. During the heights of their power they hunted vampires nearly to extinction. In order to survive vampires had to adapt to a less carnal existence, and started finding ways to hide more successfully. Thankfully as humans made advances in medical technology, methods of blood extraction became increasingly common. The Red Cross (fun fact, founded by a Sentinel) has been known to turn a blind eye to "missing" blood shipments that happen to end up with vampires.
Long lines of vampires may also have a partnership with a human family - sort of in the way noble families had ties to families of serving class folks. In exchange for a nightly meal, the vampires would offer protection, housing, and compensation. This method fell out of favor in the mid 1900's when human culture shifted away from such partnerships as well. A few do remain to this day.
Most "blood bags" of the modern era are orphans, runaways, misguided youths, etc., who end up falling through the cracks of society and get picked up by a gang of vampires in need of a feed. For most vampires a 1/2 pint of blood a day is more than enough to sustain them. Most people have about 10 pints of blood in them, so if a vampire is careful they can live off of one person's "donations" of blood. However, many vampires prefer to wait and binge, feeding once or twice a week in larger amounts.
If a vampire is without their food source - be it blood, emotions, raw meat, etc. - they begin to change. Most vampire lineages begin to develop Nosferatu like characteristics. Some vampires wither and shrivel. Regardless, consuming their food prevents these effects - though it can not generally reverse them.
Many vampires have the ability to "hibernate," where they can slow their metabolism to near stopping and appear to sleep for extended periods of time - even decades or centuries.
Magical abilities, like transforming into a bat, mist, hypnotism, etc. are generally inherited or taught to a vampire by their sire. Using such abilities tends to "burn calories" leaving the vampire hungry, and sometimes hangry.
To become a vampire, one must typically be emptied of the food source and then refilled with a vampiric food source. In the base of blood, someone must be exsanguinated and then feed off vampire blood. An emotional vampire undergoes a similar process where their own emotions are removed in their death, then they are filled with partially digested emotions from several vampires.
Shape Shifters generally meet the following three criteria:
They are not dead/undead.
An event or magical spell causes them to change into a different type of creature.
The ability to shift was conveyed by birth, infection, or magical training.
The most well known shape shifter is, of course, the werewolf. The predominant breed of werewolf changes into their wolf form during the 3 days of the full moon, and while in their wolf form, they are for all intents and purposes a normal wolf. If they were born a werewolf then their pack probably has property and may have rituals and traditions passed down through the generations regarding the change. If the person contracted the condition later in life, they may be inducted into a pack. In the rare occasion that someone is accidentally bitten and left to their own devices, they may wake up one day after a full moon to find their house has been trashed and the neighbors have complaints about the dog barking and howling all night... Some modern werewolves also use strong sleep aids to keep their wolf self asleep during the change, though this can have unpredictable results.
Lycanthropes are a variant of werewolves, likely brought into being during the 1200's by mixing alchemy and dark magic with werewolves. There was also a sharp increase of lycanthropy during the 1800's as cities became overcrowded and diseases were more easily spread. Lycans are more unpredictable and violent - not changing into wolves, but half wolf, half human creatures with immense strength. Not all lycans are governed by the moon, and sometimes they can change during heightened emotional states. Because lycans are often without a pack, they are more likely to lose control when they shift, and thus they spread more easily. Organizations like the Sentinels work to hunt down lycans and "take care of them," by whatever means are necessary. Other organizations like the Hermites and Cabal of the Eye work to help the afflicted mitigate their condition through science or magic. Some Hermites, however, seek out lycans and werewolves for less altruistic purposes....
Less common shape shifters include skinwalkers. Many Native American cultures have stories of skinwalkers who had the ability to change into animals through magical means, though the phenomena is observed in other traditions. Modern skinwalkers are careful to stay out of danger by hiding their abilities and using them sparingly. A skinwalker is not always limited to a single creature form. They can use magical items and rituals to take on other forms such as birds, wolves, rabbits, and snakes. Throughout history, the skinwalkers have used their abilities to protect tribes as well as to sow mischief and cause harm. They exist between nature and humans as well as between good and evil.