mean machine

barbarous callous cruel fierce grim harsh implacable inexorable inhumane relentless ruthless severe unforgiving unrelenting unsparing unyielding

unmerciful

compassionless cutthroat dog-eat-dog gratuitous hard hardhearted hatchet job having a killer instinct iron-fisted mortal pitiless unappeasable uncalled-for unfeeling unflinching unpitying unsympathetic wanton

bright calm compassionate considerate easy feeling flexible gentle kind merciful mild nice peaceful polite remorseful sympathetic tender yielding

giving sparing