Matchups between MLB pitchers and opposing batters will always be influenced by intimidation. More specifically, there are veterans like Kyle Farnsworth and Mariano Rivera who demoralize others with their distinct attitudes.
These masters of mental games were included and ranked with their off-the-field reputations and unique pitching tactics taken into consideration. Quality of stuff wasn't a direct factor—hence no Aroldis Chapman or Matt Harvey—though the following mound intimidators all possess great talent. Otherwise, they would not go about their business with such an edge.
As past victims and baseball writers can confirm, stepping to the plate against them is a most uncomfortable experience.