How to Make a Ghost Come Out on "Sims 3"by Seth Amery ; Updated September 22, 2017
If you're interested in adding a new ghostly roommate to your household in The Sims 3, you have a few options at your disposal. The most common way to get ghosts on your lot is to have a Sim die in your house, although you won't have control over it right away -- unless you resurrect the ghost at the science lab. On the other hand, if you have the Supernatural expansion pack, you can create ghosts in Create-a-Sim to play like a normal Sim.
Pick up the urn after a Sim dies and place it into your Sim's inventory. He'll need to bring the urn to another lot anyway, and this protects the urn from destruction should something happen to the house.
Accept the Oh My Ghost! opportunity when it appears. This special event occurs a few in-game days after a Sim dies on your lot, and only if your Sim was close to the victim. It only demands one task: Bring the urn to the science lab in your town.
If you don't know where the science lab is, you can just click the star icon that appears after accepting the opportunity. The star icon always appears on your screen relative to the direction of the opportunity building; if the science lab is north of where you are, the icon appears near the top and points up.
Head to the science lab. After a few in-game hours, the no-cost opportunity will complete and you'll have a new ghost that acts like any other homeless NPC in your town; that means you can become friends and ask the ghost to move into your home. If the resurrected Sim was already part of your household, she will remain so; however, any previous romantic relationships need to be restarted and rekindled.
You read that right: It's possible for your Sim to have a romantic relationship with a ghost. You can do this by romancing the ghost Sim just like you would any regular Sim.
It's also possible to have ghost babies. If your Sim is a female, you can use romantic interactions with a male ghost to Try for Baby in the same fashion as with a living male. If your Sim becomes pregnant, it's a coin toss whether it comes out human or ghost, and there's no way to influence the decision.
Functionally, ghost Sims are the same as they were before dying; their Needs bars degrade in the same way, and you can fill them the same way as you would with a normal Sim.
Contrary to the previous game in the series, your Sim doesn't need to know logic to resurrect another Sim.
If you want to bring a ghost back to life as a human, you'll need to feed him Ambrosia, a dish that requires the exotic ingredients Life Fruit and Death Fish.
In the Generations expansion pack, you can temporarily turn into a ghost with potions.
Playable ghosts can move out or be kicked out just like human Sims; you can kick out unplayable ghosts that wander your house at night by putting their urn into the graveyard.
If a stranger dies on your lot, you can keep the urn on your lot to allow his ghost to visit at random times, or you can take the urn to the graveyard and place the ghost to rest.