Synonyms of diabolically

3 Syllables
horribly, corruptly, brutally, wickedly, fiendishly, unkindly, ruthlessly, brutishly, callously, ferally, heartlessly
4 Syllables
hatefully, infernally, extremely, mercilessly, atrociously, barbarously, pitilessly
5 Syllables
unbelievably, barbarically, demoniacally, inhumanely, remorselessly