Becoming a Vampire
You cannot create a vampire Sim at the start of the game; you must have one of your Sims become bitten by a vampire to be transformed. Vampires are found in the Downtown areas at night and are easy to spot because they have slightly blue skin and dress like stereotypical vampires. Become friends with the vampire just as you would with any other Sim by talking to the vampire and inviting him over to hang out. Eventually, when he likes your Sim enough, he will turn him into a vampire.
Advantages to Playing as a Vampire Sim
Becoming a vampire has a number of advantages. For one, your Sim will no longer age and cannot die under natural circumstances. As your Sim no longer needs to eat or use the bathroom, his Hunger and Bladder meters will stay full. Nighttime is between 6 p.m. and 6 a.m., and during that time your vampire Sim's Energy, Comfort and Hygiene bars will also stay full unless special circumstances arise, such as getting smelly after using the weight bench.
Disadvantages to Playing as a Vampire Sim
You must purchase a coffin for your Sim immediately after becoming a vampire or he will not live to see his next evening. The coffins are located under the bed category in "Comfort" in Buy Mode. If your vampire Sim is not inside his coffin during daylight, he will die within a few hours. Another disadvantage is that vampire Sims may bite and infect other Sims when you are not directly controlling them.
Reversing the Curse
If you decide you no longer want to be a vampire, or if your vampire Sim bit one of his roommates, you will be able to reverse the curse with a special item. To cure your Sim, you must call the Gypsy Matchmaker using the phone in your house. She will arrive at your house shortly afterward and you will have the opportunity to purchase the Vampire Antidote. Drink the antidote at any time to turn your Sim back into a normal human.