There's a short story about how all the secrecy surrounding the containment of 231 is nothing but a gigantic ruse cruise by the Foundation to prevent the cult from finding out that the Foundation successfully delivered the baby, who turned out to be
999, whom they plan to use against his father once he grows up.
My favorite is
1802, a tiny golem made of garbage that collects and contains anything he doesn't understand, which is everything, made by a group of artists to parody the Foundation. They don't get the joke and in the end are tricked into containing a perfectly ordinary bottlecap just like the little trash guy does. The real magic, though, comes from the discussion page because in a glorious example of life imitating art the people on the site
also did not get it until someone made the joke clear.
Other good ones are
●●|●●●●●|●●|●, an SCP that contains no writing, and
1594, which I think is just about the most Junji Ito article on the entire site.