A description of the plane is not known.

Modrons are residents of Mechanus. Their nature is not well known, though some characters encountered a monodrome as a result of wild magic. It panicked because it was not where it was supposed to be, then disappeared.

 

There are also beings known as Inevitables, which enforce immutable fundamental laws of nature. One of those laws is that information cannot be created or destroyed, as demonstrated in 4x03 "Clear as Crystal".