Its hard, but beatable. Remember that the toughest enemy will be the clone, which is identical to your hero except that it is only programmed to attack the nearest target with whatever your primary weapon is. So I suggest not equipping powerful weapons or armor, since that only makes the clone stronger. Instead rely on secondary weapons and effects, like spells if your playing a mage, or throwing knives/bombs as an archer. You don't even need to equip a primary weapon, in which case the clone won't even attack.
Also don't forget that you have allies, try to keep them alive if you can. I also suggest that you prioritize ranged targets above melee ones, especially shamans, you want to kill those quick.
Another alternative is to go with a powerful weapon on the archer, but light on armor, and take the clone out first. It's starting health will be equal to yours, so if you start low you can often kill him while he's still targeting your allies.