In game you will see the list of names of heroes written on the ground. They are grouped depending on the faction the heroes come from. Destroy the structures to the left of the heroe's name and be warped to the stadium and face the hero. After defeating the hero you will instantly teleport to the faction group of the defeated hero. Sauron and Galadriel are also units you fight.
If you want your spellbook to be disabled, simply choose mordor for AI. If you want AI's spellbook disabled, choose men as your faction.
All heroes will use their skills to do the best way to inflict damage to opponent. All heroes with rank 10 skills(if they have) will be used.
1. If you destroy two hero structures two heroes will appear in the stadium and if you kill either one of them you will warp back to the hero list leaving the other hero in the stadium waiting for you along with the next hero you choose to face.
2. Since the hobbit heroes are weak, all four of them are summoned together and the way to get out after killing them is the statue at the back, unfortunately it cannot be targeted normally(don't know why). you will need a ranged skill of decent damage to break it.
3. There are only 2 flying heroes, Drogoth and Morgomir(mordor), you will fight khamul on foot. You don't have to worry about them flying to you IF YOU DO NOT MAKE AI ANGMAR.
4. when facing Wormtongue, if he converts your hero, just wait and he will reappear again to beat the hero up.
5. Do not use ANGMAR, it will only cause problems
My advice is to have one or two buff skills, a strong ranged skill, and heal. In general most heroes are difficult to face