When we talk about actions or events that are done with extreme atrocity, we are essentially referring to extreme cruelty, brutality, or savagery. But there are numerous synonyms that we can use to describe such actions or events. Some of these synonyms include 'barbarously', 'gruesomely', 'heinously', 'horrendously', 'inhumanely', 'monstrously', 'sadistically', 'savage', 'viciously', 'wickedly', and 'diabolically'. Each of these words conveys a sense of extreme violence, brutality, or cruelty that is far beyond what is acceptable or normal. Whether it's war crimes, torture, or mass killings, these synonyms help to underscore the severity and depravity of such actions.