Some people would do Approach in their Move Route, but that would go the WHOLE time.
An easy method in doing this would be to set a Custom Route containing Move Closer to Hero (Whatever name belongs there). A harder way would be having some common event/event trying to keep track of the distance between the monster and the hero through variables and once they are close enough with conditionals the monster switches move routes with a switch Turn on (Page 1, regular walking, Page 2, Approach). This is off the top of my head and surely it may be wrong, but who knows, who knows.