Life state

A life state or a creature is a kind of Sim with special appearance and abilities, mostly inspired by legends or science fiction.

The Sims
Life States exist in The Sims and its expansions, though not well-defined. 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, pleading with the Grim Reaper may result in him bringing a recently-deceased Sim back as a zombie. Also in 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 sometimes ends up making a zombie when she tries to resurrect a dead Sim. Servo and the Genie 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 assume the appearance of these creatures. Of course, players may choose to treat this as a temporary transformation or an illusion; the in-game effects are the same either way. The Sim who has been "charmed" is still a normal Sim, and gains no extra abilities or interactions. It could be said that witches and warlocks come with The Sims: Makin' Magic, but Sims who take up magic in Makin' Magic still look and act the same.

The Sims 2
Most expansion packs for The Sims 2 added an alternate state in which Sims can exist. Some added sentient creatures which Sims cannot become, but which can be playable Sims. These states have unique triggering techniques, advantages and disadvantages. These states are:
 * Normal Sim
 * Ghost (base game) (Not playable)
 * Alien (base game)
 * Zombie
 * Vampire
 * Werewolf
 * Servo
 * PlantSim
 * Bigfoot
 * Genie (Not playable)
 * Witch

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

The Sims 3
The Sims 3 and its current expansion packs feature 5 life states:
 * Normal Sim
 * Ghost (base game)
 * Mummy
 * SimBot
 * Vampire