- NEMESES
- Formidable opponents
- Unbeatable foes
- Bond and Blofeld, e.g.
- Fighting types
- Rivals
- Fierce opponents
- Bêtes noires
- Banes
- You can't beat 'em
- Batman and Robin, to Riddler
- Mortal enemies
- The Yankees, to the Red Sox
- Tough opponents
- Unbeatable opponents
- Archenemies
- Archrivals
- Bete noir et al.
- Waterloos
- Usually unbeatable rivals
- They can't be beaten
- Unbeatable rivals
- Luthor and Brainiac, to Superman
- They're unbeatable
- Luthor and Zod, to Superman
- Sinestro and Professor Zoom, in their respective universes
- Superheroes always have them
- They're usually unbeatable
- Foes that seem impossible to beat
- Agents of retribution
- Baddies
- They're unconquerable
- Ruins
- They can't be beat
- Relentless avengers.
- Avenging agencies.
- Embodiments of retribution.
- Avengers.
- Inflicters of retribution.
- Retributive fates.
- Fates.
- Just punishments.
- Inflicters of tribulation.
- Just retributions.
- Just deserts.
- Retributions.
- Rivals to who one always loses
- Those imposing retribution
- Thorns in one's side
- They give comeuppances
- Archenemies, maybe
- Superheroes, to villains
- Plan foilers, perhaps
- Batman and Robin, to Catwoman
- Formidable foes
- Fearsome foes
- You can't beat them
- Pokémon's Gary and Ash, e.g.
- Tough rivals
- Like Batman and Robin to the Joker
- Fierce foes
- Unbeatable archenemies
- Formidable rivals
- The Ravens, to the Steelers
- Usually victorious rivals
- Rivals who often win out
- Archenemies (note the last 2 letters of this clue's answer ...)
- The Steelers, to the Ravens
- Joker and Riddler, to Batman
- Sworn enemies
- Holmes and Moriarty, e.g.
- Agents of undoing
- Harry Potter and Lord Voldemort, e.g.
