Your "Identical" Duplicate is Really...

"You're a goody-two-shoes!"

1.) Your mystical Nemesis, birthed from the cursed, Unseelie mirror-pools of Faerie. It is identical to you in every way, save for always being the equivalent of one experience level higher than you. It is intent upon your complete and total destruction. It will, inevitably, take its sweet time making your life miserable before deigning to end your worthless existence.

2.) Your worst enemy, polymorphed to look like you, with psionic impressions of all of your memories to complete the package. Speaking of "package", wanna guess who's going to be spending some quality time with your significant other tonight?

3.) The clone abortion that's gone completely fucking sideways. Like, this thing has P R O B L E M S. Think Bizarro, if Bizarro was three shades more retarded, had extra genitals in odd places, and was prone to shitting himself in the middle of violent outbursts.

4.) It really is you, but worse. This duplicate is from an alternate universe in which you are a completely worthless shit-heel. It has -1 to all of your attributes, and is functionally one level of experience lower than you are. It might not be evil, per se, but it definitely rains douchebaggery down in heavy torrents everywhere it goes. I'm sure that won't cause you any problems.

5.) A very convincing hallucination. This good-lookin' devil is one heck of a charmer. You can't, for the life of you, understand why no one else will admit to seeing them...

6.) A Shapeshifter or Master of Disguise who's running a loooooooooong con.

7.) A random person who, for reasons unbeknownst to either you or them, just looks remarkably similar to you. Perhaps there are some family secrets which need to be aired out.

8.) A perfect illusion/hologram of your current appearance, which mimics your every action. It's offset by a distance of about 5 feet. Enemies who want to do you physical harm are going to have to take their chances, 50% chance of hitting the insubstantial copy instead of you. Dinner party conversations are likely to become very confusing, however.

9.) A perfect clone, created from a sample of your DNA . It gestates for 12 Turns before being deposited in the very same spot where you stood. It's a blank slate who will imprint on the first sentient creature it sees, like a little duckling, following them around and learning everything it needs to know about life from them.

10.) Teleporter Malfunction: You're instantly transported 10 feet to the left of where you were standing. In other news, there's another you standing 10 feet to the right of where the "accident" happened. Both characters are identical, and neither knows which one is the original.

11.) It's you from the future! This duplicate can't (or won't) reveal important details about your future escapades, or those all-important winning lotto numbers. They are, however, two levels of experience higher than you, and more than willing to help you on your current adventure. In fact, it seems like they expected to be tapped for this. The GM should keep very detailed notes about what difficulties befall this dupe, since your character will undoubtedly be called upon to endure those same problems at some point in two levels' time.

12.)  It really is you, but better! This duplicate was transported from an alternate universe in which you're just a little bit more awesome. It has +1 to all of your attributes, and is a level higher than you, but is otherwise just like you, and shares all of your goals. High-five, identi-bro!