Vampire

At the core, a vampire is an undead created from a mortal, typically passed to it by another vampire. (Exceptions do occur, see below). Vampires have a strong drive to feed on other sapient creatures, usually through drinking their blood, but some vampires aren't too discriminatory about which parts of other sapient creatures they consume.
Most vampires are stronger than their original species, and tend to gain other abilities. Some common ones include flight and the ability to polymorph into other creatures. A lot of their abilties are tied to or rely on darkness.
Vampires also tend to possess weaknesses, and the most common weakness is to sunlight. This varies from "weaker in sunlight" to "sunlight harms them if they stay there too long" to outright "single exposure to sunlight destroys them immediately." Other common weaknesses include running water, silver, garlic, the inability to enter residences without permission from a habitant, and religious symbols and blessed water (although this may just be due to their nature as an undead creature). Some tales have stranger weaknesses, such as a compulsion to count things. Many tales exist and it is hard to separate fact from fiction, a fact made even more difficult by all the variation in vampires there can be.
Another common dependency of vampires is that they sleep in a coffin that includes dirt from their own grave. The Crew was able to recount everything they'd learned about vampires and yielded some helpful information: They are weak to silver, stabbing them in the heart with a stake will only paralyze, not kill a vampire, and to ultimately defeat them (for actual realsies, so they can't regenerate), one must destroy them, remove the gravedirt from their coffin, and then sanctify the coffin.
Many mortal species are able to become vampires, though traits that they gain from this transformation differ slightly. Additionally, there may be some species that cannot pass along vampirism to certain other species, but all of the exact details are not known.