Vampire

Vampires is a new game mechanic added onto The Sims 2: Nightlife which introduces vampires as both playable and non-playable creatures to  The Sims 2 series.

Becoming a Vampire
Grand Vampires appear downtown at night and their names are preceded by either the Count or Contessa title depending on the gender. They are easily distinguishable from the crowd by their light blue skin, period clothing, and unmistakable 'bleh'.
 * Vampirism is transferred via the bite neck interaction.
 * If a Sim is bitten by the "Grand Vampire" or a pre-bitten Sim, he or she joins the world of the undead as well. Initially Sims are bitten only if they have a high relationship with the vampire, however once one Sim is bitten by a vampire any Sim that comes into contact with a vampire has a risk of being bitten, whether or not they are a playable Sim and regardless of the relationship with the vampire. Other Sims can also influence a vampire to bite another Sim.

Using the Cheat to Become a Vampire
If you want your Sim to become a Vampire without all the hassle, there is a cheat. It's much easier than trying to find the "Grand Vampire" and the cheat enables you to make your Sim a Vampire in any of The Sims 2 expansions as well as The Sims: Life Stories.
 * Press "Ctrl" "Shift" "C" to open up the "Cheat Window" either in the neighborhood, or on a lot.
 * The cheat is boolProp testingCheatsEnabled true
 * When you have the cheat enabled, just hold the "Shift" button down while you "Left Click" on the Sim you want to turn into a Vampire. Many new options will appear. Find the option that says "Make Vampire". Your Sim will instantly become a Vampire. You can also cure your Sim from Vampirism without the hassle of buying a "Cure Potion" by using the same cheat.

Features

 * When a Sim turns into a vampire they receive the characteristic sharp teeth, red eyes and pale skin. Aliens turn turquoise, Zombies turn dark blue! Servos also can become vampires, with red eyes and fangs.
 * Once bitten, the newly created vampire can bite other Sims.
 * Vampires can transform into bats and fly around, which allows them to fly over low obstacles such as kitchen counters and is a fast alternative to walking for Sims too lazy to run. Vampires can also 'stalk' from place to place.
 * Vampire Sims gain the Irritate > Bleh! interaction which lowers the Bladder need of target non-vampire Sim and can be used regardless of relationship.
 * Vampires will sizzle and smoke while exposed to the daylight, and their motives drop very quickly, eventually leading to the vampire's demise. Motives will also slowly decay indoors, or more quickly if they're near a window. A vampire Sim must sleep in his/her coffin or meditate during the day to prevent their needs from dropping.
 * For this reason, vampires are contactable at night but not during the day without drama.
 * The motives of a vampire Sim do not decay at all during the night. This is meant to give them plenty of opportunity to party Downtown all night. They still lose needs when doing some activities.
 * Another additional feature is the fact that the vampire Sims are immortal and will never grow older than the day they were bitten, with the exception of the transition from Teen to Young Adult to Adult.
 * Even if Hunger reaches 0, vampires will not die of starvation.
 * Vampires have no reflection in a mirror. If one is used, the vampire will react and their comfort bar will drop. Disturbingly, while vampires are invisible in mirrors, their wedding rings are not.
 * Occasionally vampires will hiss or go 'bleh' if no other action is currently underway.
 * Vampirism is viral, not genetic, so even if two vampires have a child together the baby will always be human.
 * Vampires can also become werewolves. When they become one, they will look like vampires in the day and werewolves at night. They can bite and savage as well as fly and stalk.

Re-"Normalization"
If at any time the Sim grows tired of the vampire life, Vampirism can be cured with Vamprocillin-D which is bought from the Gypsy Matchmaker. The Sim will be able to go out in the day but will lose all the perks of being a creature of the night.

Wanting and Fearing Vampirism
All Sims except Knowledge sims will fear vampirism, and said knowledge Sims will want it, and once are bitten will fear curing it.

Speculation

 * Vampires may be included in The Sims 3.