@AlienTusks Ghosts will visit whatever lot their tombstone is on, usually at around midnight. They don’t come every night, though, so you have to be persistent. When you see the ghost, you can interact with them. Increasing your relationship with them will give you the option of adding them to your household, which makes them playable. If you don’t want them around, you have the option of selecting “release to the netherworld.” That essentially culls the ghost NPC. With time, a ghost that’s not played or interacted with will be culled. The “spirit fading” message is a warning that the ghost is losing its connection to the human world and will be forever gone if there isn’t any interaction. You can help by selecting “strengthen connection to physical world” on the tomb. To move the tombstone, see if it will let you put it in your sim’s inventory. Sometimes that works for me, other times it doesn’t.
If you want to go the route of resurrecting the ghost, there are several ways in game to do it. You can have a sim learn how to make ambrosia and have a ghost eat it, which will restore their life. A ghost sim can wish for life at the wishing well from the Romantic Garden pack. If you have Realm of Magic, a spellcaster can cast Necrocall to bring the ghost from the grave and Dedeathify to return the ghost to life. To prevent losing future sims, have a sim complete the best selling author aspiration. This unlocks the ability to write the Book of Life and bind it to a sim. It can then be used to resurrect them if they die.
