Ruins

The Ruins of Whomp's Fortress, usually shortened to Ruins is an anomalous level in Super Mario 64. This level only appears in certain personalized copies of Super Mario 64, and has only one documented report. This report is a YouTube video from January 21, 2021, showcasing Mario in a level that is eerily similar to Whomp's Fortress.

Upon entering the level, the audio for solving a puzzle plays. It's unknown why this happens, but a common theory is that the level was originally a secret level before turning into an anomalous zone.

Strange Occurrences
When the player begins climbing up the tower, they find a buggy version of MIPS that has a bubble on top of it.

It's possible that a Piranha Plant was swapped with MIPS' model, causing the buggy appearance. Mario also meets a pink Bob-omb on the top of the Ruins.

Pink Bob-omb
"Mario! Am I glad to see that you're still in one piece!

Oh, right, you don't know what this place is. This, er, was Whomp's Fortress. Now it's just a hollow shell. This area's previous residents have had their bodies deformed and torn up.

It's not long before it comes back, and comes for you.

I'm sorry I couldn't save you...

Goodbye."

It's unknown what the It the Bob-omb is talking about is, and no theories have surfaced due to how cryptic it is. Some people claim it's the White-eyed chomp, or the Wario Apparition, but none of these theories have any evidence.