A fairy.
Don't judge me.
I'm making a fantasy scenerio, and I was thinking of what would make a good explorer/spy type unit for the elves. My mind kept wandering back to the Midgard fantasy expansion to Civ 2. I don't know if anyone's ever played it, but the spy unit was a fairy. It made sense; the fey have always been seen as both elusive and mischevious, and with a few fairies and a ton of gold, a civ could wreak havoc on his neighbors. Those invisible faries would flutter cutely from city to city, stealing techs, sabotaging production, and inciting bloody revolutions wherever they went.
If someone could just convert the old Civ 2 fairy, I'd be happy with that, too... but, of course, a brand new one would be better.