iT he move is called the "free ride".once an enemy is down ,u jump over him in a way that will make u stand on him.Then use the left analog syick to control the direction of ur ride on the enemy.
To bring down an enemy hit moves like helm breaker (rebellion) or lift the enemy in the air .Eventually he will lie flat on the gorund.then u can execute free ride by jumping over him.
If u have any doubts regarding the moves ,press start menu when u r in the mission.
goto status,select file from that menu.
u will find a list from which u can select and watch the combos that dante can make.
one of the option is "style" where u can see different moves in each style(if u level them up)
The other option is the "devil arms".press x and u will find different moves that dante can do.
u can perform "free-ride" in any style.It does not depend on which style u r in.