The Noclip Room

The Noclip Room is a hidden room in some personalized copies of Super Mario 64. It is a room that uses the beta castle assets, some stairs leading to a raised platforms, and a panel on the wall says "how'd you fucking noclip" along with a cat, similarly to the Cat Room. It is found by somehow glitching behind a bookshelf, hence the name. It is believed it was an Easter egg in the earlier builds of Super Mario 64, but was removed due to profanity.