fiendish (adj.)

• animal
• anthropophagous
• atrocious
• bad
• baleful
• barbaric
• barbarous
• beastly
• bestial
• bloodthirsty
• bloody
• bloody-minded
• brutal
• brute
• brutish
• cannibalistic
• cruel
• cursed
• damnable
• demoniac
• demoniacal
• demonic
• devilish
• diabolic
• diabolical
• evil
• execrable
• fell
• feral
• ferocious
• fierce
• ghoulish
• heinous
• hellish
• infernal
• inhuman
• inhumane
• malefic
• maleficent
• malevolent
• malicious
• malign
• malignant
• monstrous
• murderous
• outrageous
• ruthless
• sadistic
• sanguinary
• sanguineous
• satanic
• savage
• serpentine
• sinister
• subhuman
• truculent
• unchristian
• uncivilized
• ungodly
• unhallowed
• unhuman
• vicious
• wicked
• wolfish