The SCP Foundation is a secret organization dedicated to securing, containing, and protecting various anomalous entities. The website is an archive of top secret documents including entries for each entity, called an SCP followed by a number, containing a practical name, detailed description, the effects of the anomaly, experiments performed, containment methods, pictures, etc. Objects can be anything, benign looking household items, monsters, seemingly normal humans, etc. There’s nearly 5000 entries on the site. It’s a pretty fun time sink if you’re into short horror stories. Most of them only take a minute or two to read. There’s also multiple games, most notably SCP Containment Breach and tons of spinoff material.

come up with a weird supernatural concept and write it in the format of a lab report

SCP-80085
Special Containment Procedures: put it in a secure room and don’t fucking touch it.
Description: SCP-80085 is a McTasty burger as served by the McDonald’s restaurant chain, seemingly immune to rot and decay. Anyone who touches it fucking dies instantly from clogged arteries causing a heart attack.
Addendum: Somehow Steve survived touching the burger, he took a bite and fucking exploded when he swallowed it, holy shit that’s gonna take some therapy. Burger seems to have regenerated though.

A creative writing project where the stories are all loosely based in a common universe where there is a secret organization protecting humanity from an evil force which manifests as a broad variety of different monsters.

Google it. It’s pretty fascinating.