If “A Feint Plan” is activated and you control only face-down monsters, your opponent cannot attack any of your monsters and they cannot attack your Life Points directly either.
If you activate “A Feint Plan” after your opponent declares an attack against one of your face-down monsters, that attack resolves as normal, but they cannot attack other face-down monsters for the remainder of the turn. (This is because “A Feint Plan” prevents declaring an attack against a face-down monster, and the attack has already been declared by the time “A Feint Plan” resolves during the Battle Step.)
Netrep Rulings:
If “A Feint Plan” is activated in response to an opponent’s declaration of an Attack on a face-down monster, that attack will resolve normally.
If all of a player’s monsters are face-down in the turn that “A Feint Plan” is activated, the opponent may not attack directly, unless the attacking monster can inherently attack directly, such as “Inaba White Rabbit,” “Jinzo #7,” a monster equipped with “Shooting Star Bow – Ceal”, or Toons.