Who are the good guys and who are the bad guys?
Short answer: The Ustashi.
The Croats were allied with Nazi Germany and the Croats had their own “bad guys”, the Ustashi.
The “bad guys” are the Croatian “Ustashe” (worse than the German Nazis, even by official accounts) and the “good guys” are all the innocent Serbian civilians and Serbian Orthodox clergy, etc. that were their victims.