Example sentences:

Ramayana:  Vibhishana warned Ravana that the same Visnu who had been the nemesis of demons since time immemorial, had now descended as Rama to be his nemesis.

Mahabharata:  Karna longed for an opportunity to defeat Arjuna who had been his nemesis for decades.

Bhagavad-gita:  As long as the mind is uncontrolled, it remains the soul’s greatest nemesis.