It's not my idea, so i can post it Maybe some of you have played Diablo3. There is an opponent called shadow warrior which has same strenght and skils as your character.
So how about a monster 'boggart' a shape shifter that will transform into the player (not summon) that it first makes contact with. It will have the same attributes, same perks, even same armor as the player, only 10 times the original health (that is with crown of life) . What is so interesting about this monster is that this monster will be avoided by the strongest fighters. First, you never want to fight yourself. Some players are so proud they can make extra high damage with special weapons and Fire arrows. It would be really fun if it turns against them
Ok it wasn't my idea, i don't take the credit. And if you think it's a really stupid idea, .. was not me ^,^-