I want to add a couple of good ones I’ve found:
Jeff the Killer lost media: no one knows where the original Jeff The Killer image came from.
Mortis.com: old weird website
Also here’s a good website on various obscure computer/Internet related oddities: https://suricrasia.online/iceberg/
Yeah, it’s fun to laugh at these weird theories, but a bit depressing when you realize a lot of them come from a place of serious mental illness.