Aliens are already in the packs base.
Zombies require the University expansion pack.
Vampires require the Nightlife expansion pack.
Servos require the Open for Business expansion pack.
Werewolves require the Pets expansion pack.
Plant sims require the Seasons expansion pack.
Bigfoot requires the Bon Voyage expansion pack.
Genies requires the Free Time expansion pack.
Witches requires the Apartment Life expansion pack.
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