The Heine NPC, trion, says:

Once before -- I do not remember when exactly -- I tried to go to Aden. Then I lost my way and ended up in the Forest of Mirrors. I thought I would just die then and there because ferocious monsters were roaming everywhere. Thinking about it now, I believe surviving the ordeal was a miracle. But the scariest experience was meeting doepelganger[sic], a monster that looks exactly like me. I still have nightmares about it.

So, I ventured out into the Forest of Mirrors searching for my doppelganger. Well, not only did I run into my doppelganger (pictured to the right after killing me), but I ran into *other peoples* doppelgangers. I ran into an elf, and even a skel morph of someone. I even at one point had three Amers on the screen! Imagine hunting with your friend and thinking "well, why is my friend running at me - OH NO, THATS NOT MY FRIEND!" A doppelganger probably does not have its own shape, it morphs into the first person it sees. I'm not sure what the stats are on a doppelganger, but I had wielded a trident and my doppel had a sword of some kind, so its possible that its not a spitting image of you.

The really cool thing is that when you see a doppel, you can't be sure if its a doppel or the actual person, so you are tempted to run up to it and kill it. Well, if you do, the other person (who might be real) might think you are a doppel and run to you! So you might be killing each other and then find out you just PKed and thought you were attacking doppel! Such wondrous confusion!