Okay, I read Off the Edge of the Map. Brilliant fic, and gives me a good idea of what this is all about.
Character-wise, I think I'll avoid Elixir. I'd like to get a chance to play him, but in my mind he's a seasoned adventurer (perhaps not a great one, but he knows how to fight) and so I'm not sure if he'll fit the tone.
I do have a vague sort of idea for a character, though. City Slicker, a tour guide for Canterlot or maybe Manehatten. Probably an earth pony. He knows the city like the back off his hoof, knows everypony, street smart, always very sure of himself. Away from the big city, he'll be out of his depth, but might make a good fast-talker for when the group reaches some form of civilization. Will probably have a cockney accent.
He might know the group because he took them on a tour once, or maybe he just met them at some event. Cutie mark would be something like a hoofprint on a cobblestone path, or possibly a city skyline.