Everythi---
God damn it Kup.
I usually sit down and have my laptop ready to find reference images for anything, or a pile of pre printed references ready to go because I can pretty much not draw anything from memory, at all, except people...
I have a hard time drawing:
Perspectives, cities, buildings, foreshortening, backgrounds, movement, actionscenes, hands (occasionally :I), really really eccentric Edwardian clothing, anything mechanical or technical (gears, machines, vehicles, etc.) Proportions.
um
but I am all right with most animals? Maybe :L