Life state

The Sims 2
Each expansion pack for The Sims 2 released to date has added an alternate state in which Sims can exist. These states have unique triggering techniques, advantages and disadvantages. These states are:
 * Humans (or Sims)
 * Ghosts (base game)
 * Aliens (base game)
 * Zombies (University, FreeTime, Apartment Life)
 * Vampires (Nightlife)
 * Servos (Open for Business)
 * Werewolves (Pets)
 * PlantSims (Seasons)
 * Bigfoot (Bon Voyage)
 * Genie (FreeTime)
 * Witches (Apartment Life)

Each life state offers new opportunities for the Sim, making certain aspects of play easier to handle and others harder.

However, all above creatures that appeared in The Sims 2 were also in The Sims or its expansions. In The Sims: Livin' Large, there is purple potion which can turn your Sim into a monster. Also there are ghosts and zombies, and in Sims Unleashed there is Palm Read Lady which can cure zombification. Aliens are there every night, sometimes they take Sims who use telescopes. Genie and Servo were added in The Sims Livin' Large, and they look very similar to these that comes with The Sims 2: Open for Business and The Sims 2: FreeTime. Werewolves, vampires, PlantSims and Bigfoots are added in The Sims: Makin' Magic. When a Sim makes the Beauty or the Beast charm and then use it, he/she can be transformed in any creature from this list and much more. But when they are transformed, they still have the same abilities like normal Sims. Witches and warlocks comes with The Sims: Makin' Magic, and there is a whole new world for them.

The Sims 3
The Sims 3 and current EPs feature only three life states, Humans, playable Ghosts (base game) and Mummies (World Adventures).