Follow the path, take note of the objects that you can pick up by smashing the boxes with the Square prompts.
Wait until the dragon smashes its head in the ground and is dizzied, hit it 3 times. It will recover and you need to wait until it bangs its head again. Rinse and repeat.
Stand at the baiting platform, wait until the Witch-King strikes, jump away to avoid the strike, then hit him when his weapon gets stuck. You need to do this 2 more times, there is another platform you need to build on the right and another one hidden by smashing the items on the lower left area. Switch Characters, stand behind the Witch-King, then hit Circle during the choking scene.
You need Aragorn and Legolas to defeat the oliphaunts. Some oliphaunts have red rocks on their feet, just smash them with Aragorn, then mash Square. For the others, use Legolas to shoot the two targets on their legs on one side of their body, jump up the bars on the legs, jump up the ropes, climb up to the top and beat the riders.
Use Legolas to shoot the targets along the way as you follow the trail.
Stuck on trying to shoot targets on legs and how do you stop the attacker when you want to shoot targets