Inferno faction discussion.

Improved - an exact copy of the unimproved version, but completely engulfed in flames. Although this was also the case in "part 5".

In my opinion, there haven't been any exceptions so far when comparing the published artwork. For the improved version, they simply add some extra details, slightly recolor it, and that's it. In the fifth part, it's mostly the same. And probably in the third part as well, with a few rare exceptions.

on Facebook, there's the unimproved Fiend of the Dungeon.

fiend [fiːnd] 1) devil; demon 2) villain, fiend

"Fiend" is, of course, the most logical and suitable translation of the word Fiend among the possible options.