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 the above creatures that appeared in The Sims 2 were also in The Sims or its expansions. There are ghosts. While aliens are not seen, they are there, and may abduct Sims who use telescopes at night. In The Sims: Livin' Large, Sims using the chemistry set might make a purple potion that will temporarily turn a Sim into a monster.

In The Sims: Unleashed Miss Lucille of Old Town, who sometimes ends up making a zombie when she tries to resurrect a dead Sim. The Genie and Servo were added in The Sims Livin' Large, and they look very similar to those that come with The Sims 2: Open for Business and The Sims 2: FreeTime, though Sims 1 Servos are objects and not playable Sims.

In a sense, werewolves, vampires, PlantSims and Bigfoots are added in The Sims: Makin' Magic. When a Sim makes the Beauty or Beast charm and then uses 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).