On the Barrow-downs level, after you have moved through the graveyard and killed all of the whispy ghosts, you will arrive in a cave. Merry, Pippin and Sam are in the back, and a Barrow-wight will be guarding them. Do not move toward the hobbits, or the wight will begin attacking you. Instead, move forward and onto the ledge on the wall opposite yourself. Open the chest and you will recieve a Westernesse dagger. Use this to chop the wight. After about nine hacks Tom Bombadil will show up and eliminate the enemy. Tip: Use the Ring when you hack so the wight cannot attack you.