(role of) the villain (in theatre, etc.); the bad guy

slander; bad-mouthing; abuse; insult; speaking ill (of)

atrocious; heinous; fiendish; brutal; vicious

difficult to ...; hard to ...

deterioration; getting worse; worsening; aggravation; degeneration; corruption

worst

malicious; vicious; malignant; underhanded

Māra; evil spirits or forces that hinder one's path to enlightenment

nightmare; bad dream

vicious circle; vicious cycle

badness; mean mischief

hatred; abhorrence; loathing; detestation