If you read the Order of the Stick webcomic (which I highly recommend — it’s great in so many ways), you’re familiar with the Linear Guild — the NPC foils to the main characters, the Order of the Stick.

The Linear Guild is essentially an evil version of the Order, right down to their D&D class roles — much like Link (in the Zelda videogames) always has to fight an evil copy of himself, or the Mirror Universe versions of themselves that Star Trek crews are always running into.

In those media, evil counterpart characters are a lot of fun. Their authors and creators take care to use them well, and a bit of humor (or more than a bit, for OotS) is involved. But does this concept translate well into RPGs?

Would your players enjoy occasionally fighting, or scheming against, evil versions of their PCs? Or would the similarity in abilities — and the obvious metagame aspect — get on their nerves?