internecine (adj.)

• baneful
• brutal
• calamitous
• cataclysmal
• cataclysmic
• catastrophic
• consuming
• consumptive
• deadly
• deathly
• destroying
• destructive
• devastating
• disastrous
• fatal
• fateful
• feral
• killing
• lethal
• malign
• malignant
• mortal
• nihilistic
• pernicious
• ravaging
• ruinous
• savage
• self-destructive
• subversive
• suicidal
• virulent
• wasteful
• withering