How do you marry a ghost on sims 3?

Answer 1

First get the Oh my Ghost opritunitie " harder when you have lots of skills " to increase the chanse of that become good friends at least with the ghost you want to marry then you should get it as long as you don`t have any more special oppritunities currently to do.

then bring the urn to the science lab and then treat the ghost like a normal sim and marry it.