1) The lone Ringwraith was set up as a distraction for the Dunedain, hoping that they would be easier to defeat if their forces were split. It skirts the edge of the forest.
2) The Witch King and the other Wraith move forward.
3) Some of the Dunedain head towards the single Wraith to cut it off
4) Other Dunedain move to intercept the Witch King and friend.