They simply add some extra features to the improved version, slightly repaint it, and that's it. In the fifth part, it's mostly the same. And probably in the third part too, with a few exceptions.
fiend [fiːnd] 1) devil; demon 2) villain, scoundrel
"Villain" is the most logical and suitable translation of the word Fiend among the possible options.
Yes, the most suitable one; it just can't be "devil of the pit" or "demon of the pit" – it doesn't make sense.;)
Added 1 minute ago
And in general, I would like to see the return of the Ifrit.
Демократия есть одурачивание народа при помощи народа ради блага народа.(Уайльд Оскар)