I would have assumed Eithan would be hard to write because coming up with wit that feels real and genuine requires you to repeatedly create unique, context-dependent inventions of language, rather than just falling back on cookie-cutter patterns and stock phrases.
P.S. I really hope this won't be the last we see of Eithan as an important character in the series. I really want to see him being a smart-ass in his trial and his interactions with the other judges.
P.P.S. I'm forgetting the exact line, but my favorite Eithan moment was during the uncrowned tournament (I believe the fight for the crowns in the second stage) where he says something like "I really must insist that we go back to murdering each other in the spirit of the competition." (Heavily paraphrasing).
I have a (relatively) professional demeanor when dealing with fans, but as a person, almost everything I say is a joke. Responding to things seriously is out of character for me.
So part of what makes writing Eithan easier is that I’m more comfortable writing jokes than serious dialogue.
Another part is that I’ve been sitting on the character since I was in college, so I have a great understanding of his personality and can write in-character for him without thinking.
P.S. Minor spoilers for Dreadgod: Currently, the prologue of Book 11 is the Trial of Ozriel.
P.P.S. That’s one of my favorite one-off Eithan lines too. Probably my favorite joke, and the one I was looking forward to the most, is him throwing the match against Yan Shoumei in Wintersteel.