Related Clues:

• Plan foilers, perhaps
• Competitors
• The other side
• Opposite sides
• Ruins
• 'Them'
• They're unconquerable
• They may be bitter
• Opponents
• 'Wise men learn much from ___': Aristophanes
• Batman and Robin, to Catwoman
• Antagonists
• Ones at the gate, maybe
• Some are bitter
• Fierce foes