merciless
unmerciful
Draconian
Tartarean
animal
anthropophagous
atrocious
barbaric
barbarous
beastly
bestial
bloodthirsty
bloody
bloody-minded
bowelless
brutal
brutalized
brute
brutish
callous
cannibalistic
cruel
cruel-hearted
demoniac
demoniacal
devilish
diabolic
dog-eat-dog
fell
feral
ferine
ferocious
fiendish
fiendlike
fierce
flinty
hard
harsh
heartless
hellish
implacable
inclement
inexorable
infernal
inhuman
inhumane
kill-crazy
malign
malignant
mean
aggressive
bold
murderous
reckless
remorseless
resolute
unscrupulous
toothless