Quickest and best way to get this is start mission 1.2:And stay out. When mission starts go up the stairs to the right and drop down the far side, run past the group of enemies. one will follow so throw him of the ledge. Near there there are 3 archers and past them 6 warriors throw them off the near by ledges. After your done with them go to the opposite side and climb the ladder and throw those archers and warriors off the ledge. Now restart mission and repeat 2-3 more times. Shouldn't take no more than 10-15 mins.
For reference, to throw an enemy a ledge press
, you also use the
+
to choose a direction throw them in.