How To Defeat The Cave Troll

When the Cave troll, first enters it breaks a post and the stones fall to the ground in a pile, build them up to make a platform, you mat need to run away from the platform so the troll follows you and you have time to build it and jump on top before it breaks it. Use Legolas and double jump over to the ledge and build up the fallen post with the grey blocks and the cave troll will swing he chain at you and get it caught around the post. Jump on the chain and walk to wards the trolls head and it will automatically soot arrows in it's head and break the post. Switch to Gimli and build up the grey stone to make stairs and walk up onto the ledge. Walk left and jump on the platform and jump and hit the attack button to break the slab (you will need Balin's axe which you can find behind a spider web when you first enter the tomb) and go through the crawl space when you emerge, head left and break the slab at the end and the build up the second post with the rubble left fro the slab. Stand behind it and hold the attack button to do a charge attack on the post, it will fall on the trolls head and killing the troll!
Hope this help!