Examples
Vampires
The curse of vampirism creates a cannibalistic urge in the victim. Ordinary food loses its taste, and the victim is compelled to seek out the flesh, blood, and bones of their own species in order to satiate themselves. They also have a sensitivity to sunlight. In exchange for fulfilling these conditions, vampires are granted a wide range of supernatural abilities— including life spans that border on immortality.
Sensitivity to the curse increases with age. A twenty-year vampire can resist feeding without consequences, and has a mild sensitivity to light. At seventy years, feeding becomes a necessity, and direct sunlight can cause burns within an hour. At two hundred years, feeding must occur every day, and any exposure to sunlight begins an immolation process. Most vampires will live to be at least 150 years old.
The vampire curse germinates through blood. An ordinary human must drink 2.5 fluid ounces of germinated blood in order to become a vampire— roughly two shot glasses' worth.
Vampires are often compared to witches for their versatile set of abilities; coincidentally, there are several long-standing feuds between vampires and witches, with the two factions being (literally) at each other's throats for most of Anotherworld's history.
Therianthropes
The curse of therianthropy combines a human's soul with that of an animal. The victim is exposed to feral urges after just a few days, and experiences a total transformation within a matter of weeks— they may remain in this animal transformation for a long time, waiting for their body to adjust to the experience. After the acclimation process, they change back and forth when they are exposed to specific triggers. The most common type of therianthropy is lycanthropy, and the most common transformation trigger is the full moon.
Each transformation brings the victim more in line with both of their forms. Advanced therians gain an awareness of their actions while in animal form, enhanced physical abilities in their human form, a resistance to the transformation, and even the ability to change back and forth at will. Even if their animal form has a short lifespan, therianthropes tend to live long lives. The increased blood flow and regenerative traits required to survive the transformation results in a life expectancy of about 100 years old.
The therianthrope curse germinates through normal animals. If a therian bites an animal, the curse will spread to that animal. (It does not affect the animal in any way.) If that animal bites a human, then the curse will spread to them, creating a new case of therianthropy. It is the animal that determines the shape of the curse, not the curse bearer or the victim— a rabbit that has been bitten by a werewolf will germinate rabbit therians.
Therianthropy is often confused with other forced transformations. If the transformation into an animal is caused by a spirit, it is known as zoanthropic possession. If the transformation into an animal is caused by a mythical patron, it is known as a lineage.