Have you not noticed Shiftry's pokebody? If your opponent flips a coin during their turn it's always treated as tails. So they're stuck confused and not able to attack.
Well yeah things like that are always in effect but still, it makes Shiftry a good lock deck. Besides less and less people are using Dialga G or Unown G these days and you can use something like Dugtrio PL or Ariados MT to try and stop retreating.