not a variation of “the man in the arena,” but a term from the world of cryptography.  It’s the technique British magician Derren Brown used while playing 9 others in games of chess, to come out on top.  This is the video of the performance:

Not that’s impossible to do so without trickery - this is an old picture of the late Bobby Fischer:

the example I remember of the man-in-the-middle attack is that of the South African air force.  Each airplane has a transponder on it that’s used to identify-friend-or-foe - yet an enemy side can impersonate them by intercepting the signal, relaying it to another South African station, recording their response, and replaying it to the airplane.