@Meddler: When it comes to making a duelist Champion, what do you feel are critical points?

League's more recent attempts at pure duelist Champions, IMO, haven't really been that successful (if Fiora and Aatrox are anything to go by). Either they find abusive side cases, are left without good counterplay, or something else screws them up and forces nerfs. I know League is meant to be a team game, but there need to be some fighter Champions designed to dominate 1v1 conflicts.

Since Fiora and Aatrox get too much AOE as duelists, I feel that a true duelist needs to lack a good ability to deal damage to multiple threats at once, and instead focuses on engaging and destroying one target at a time. Dueling generally means slugfights too, so you gotta get durability through combat, not through holding back and waiting around like a Gayren. Fiora and Aatrox had the right approach in those regards, but are undertuned intentionally because their methods lead to potentially infinite sustain.

(Did I miss anything important?)

Well, I've tried my hand at it, going with a direction that I don't think you've taken yet: an AP-based autoattack duelist. She specializes in rapid on-hit magic damage and gets her durability through shields on every 4th consecutive attack (no sustain, but she has superior trade power in extended duels).

Here's the link if you're interested: http://boards.na.leagueoflegends.com/en/c/skin-champion-concepts/aGuGtOEQ-celes-the-hand-of-justice http://imgur.com/Y1M2U2e

If anyone else is interested in critiquing, go right ahead.