All fiendishly synonyms

adverb fiendishly

• cruelly — willfully or knowingly causing pain or distress to others.
• inhumanly — lacking qualities of sympathy, pity, warmth, compassion, or the like; cruel; brutal: an inhuman master.
• brutally — savage; cruel; inhuman: a brutal attack on the village.
• maliciously — full of, characterized by, or showing malice; intentionally harmful; spiteful: malicious gossip.
• wickedly — evil or morally bad in principle or practice; sinful; iniquitous: wicked people; wicked habits.
• villainously — having a cruel, wicked, malicious nature or character.
• barbarously — uncivilized; wild; savage; crude.
• malevolently — wishing evil or harm to another or others; showing ill will; ill-disposed; malicious: His failures made him malevolent toward those who were successful.
• monstrously — frightful or hideous, especially in appearance; extremely ugly.
• extremely — To a very great degree ; very.
• excessively — To a greater degree or in greater amounts than is necessary, normal, or desirable; inordinately.
• extraordinarily — In an extraordinary manner.
• incredibly — so extraordinary as to seem impossible: incredible speed.
• impossibly — not possible; unable to be, exist, happen, etc.
• horribly — causing or tending to cause horror; shockingly dreadful: a horrible sight.
• hellish — of, like, or suitable to hell; infernal; vile; horrible: It was a hellish war.
• diabolically — having the qualities of a devil; devilish; fiendish; outrageously wicked: a diabolic plot.
• unbelievably — too dubious or improbable to be believed: an unbelievable excuse.