External Plexus

The External Plexus is a theory that the outside areas of Princess Peach's Castle, the Castle Grounds and Castle Courtyard, are actually vital components to the personalization A.I. It is the opposite of the Internal Plexus theory.

Castle Grounds
It is believed the Castle Grounds is important to the A.I. due to being the starting area of the game.

Castle Courtyard
It isn't agreed upon why the Castle Courtyard is important, though the most common explanation is the L Is Real 2401 statue, and it's ties to Luigi and the L is real 2401 theory.