I write my comic, so I asked my partner what was the most challenging for him.
He pointed to this one:
It's one of the last ones he did. It's not even released yet, actually.
He said it was hard because: 1) He hates backgrounds and for the first time it was one he couldn't get references; 2) He couldn't draw normal people as extras and he didn't do any designs beforehand; 3) Perspective is a tricky thing; 4) New setting for the first time, basically.
I strive to complicate his life even further soon.
@Velome It might be considered a failure, looks super sick though