This is the easy way to kill the balrog of morgoth:
In 2-player campaign, one person be the archer, the other the scout. Have the archer only use fire-arrows on the balrog while the scout tosses fire bombs. For some reason, the fire does more damage than anything els. This will kill him in only a couple of hits.
The witch-king can be killed very easily in any game type. Become a scout and follow the king into the middle of a battle. When he is busy killing other people, walk up next to him while invisible, and backstab him.
aragon-hold heavy attack for5 seconds and press light attack while holding heavy it will make you heal over time and be faster and stronger
Legolas-hold light attack for 5 seconds and jump while holding light he will ride his shield
Eowen-press light attack them jump immeidietly to jump above an enimes head