One family at a time, I had to save my sims to the library bin (if I could--sometimes that didn't work) or the CAS bin, and then settle them in other worlds. So, I opened up that glitchy Riverview world ONE LAST TIME to rescue a couple of simbots. Trust me. There is nothing that would motivate me to open this save ever again!
After freeing the last of my sims from that nightmare world, I happened to see an odd thing about the Malloy family. I wasn't sure what it was, so I followed them and opened their house to check. Thank goodness I'd already saved this family to the bin several weeks before then.
This is Laurel who used to be Laurel Grisby before a nose job and a marriage to Quin Malloy (one of my sims).

She looks quite normal, right? Now, Quin and Laurel have a toddler son named Luis. I found Quin upstairs putting him into the crib. Take a look at this... oh, and prepare yourself for a shock!
Luis has turned into a clone of his mother!

Yes, Luis the toddler is gone, replaced by a YA daughter (still named Luis) who looks exactly like her mother. I have never seen anything this freaky in game before!

Miss Luis popped out of Dad's arms and walked downstairs where her mother was. I checked the family tree so I know this new invader is suppose to be a YA daughter of the Malloys, but she's the same age as her "mother."

Luis and Quin started listening to Laurel on the piano, eyeing each other in a very strange way. And Quin was still holding his arm as if carrying a toddler.

I tried several resets, but Quin and Luis just walked back into the house to listen to Laurel's music. Quin's arm relaxed, but that was it. The whole thing just gave me the creeps. Luis' expression! So I closed out the game without saving. Yikes! Good-bye forever old Riverview. Thanks for the memories.
