I'm working on my campaign and we actually get to play twice this week (Labor Day in the States) and I'm having some writer's block. Originally I planned on homebrewing my own Infernal Duke out of a Pit Fiend, but I'm not doing so well with it.
I did find this guy. But he's not a pit fiend.
My party is APL 22.5, and I expect them to have to fight two or more pit fiends straight from the book before this boss fight. (All together this adventure oughta take them to level 17 and Mythic Tier 6.)
Are there any really good Infernal Duke builds out there?