During "The Battle of Pelennor Fields" you will face off against 2 waves of Oliphaunt the first has 2 and the 2nd has 3. 1 in each wave has spots where you have to shoot arrows into it and use them to climb. I used Legolas to shoot the arrows then go up the Oliphaunt using the arrows, then climbing the rope hanging down. Defeat the enemy on the very top of the rig on top then stand near the front of the basket and press O to kill it. Trophy pops.