I'll post this here first: there is or was a glitch / easter egg in the first SIms game (r at least the Macintosh version) where you could have a Ghost Sim that you could control. I'm not sure how exactly I did it (they always had fire eaths though, maybe that was part of it?) but I did it as early as 2002 but it was probably in 2001; the first time I did it, I did not have any expansion packs installed and I would get the expansions as soon as I could. There was even an option for your ghost sim to haunt the lot if you clicked on the grave marker / urn and selected "Ghost Walk." "Ghost Walk" doesn't sound like it was changed from developer mode.
The last time I looked this up a few years ago, nobody had this on the Sims Wikipedia although I tried posting about it there. This should be known. Dated October 24, 219 at 3:19 AM EST.