|This article is a stub. You can help Yugipedia by expanding it.|
The low-Level members are named after conservation biology terms, while Level 11 members modify the theme name into "Archnemeses" and are named with the Greek words for "first" and "last". The theme itself might be a reference to Nemesis, an hypothetical star orbiting the Sun at the extreme edge of the Solar System that was proposed as possible cause of Earth's mass extinctions by way of pushing asteroids into the inner system.
The "Nemeses" theme focuses on summoning the Level 11 "Archnemeses" monsters, "Archnemeses Eschatos" and "Archnemeses Protos", and using their effects to destroy all monsters of a specific Type ("Eschatos") or Attribute ("Protos") and locking both players from Special Summoning monsters of that Type/Attribute until the end of the next turn, which can be devastating against Decks that utilize key monsters of a single Type/Attribute. Both "Archnemeses" monsters are Special Summon-only monsters that require banishing 3 monsters with different Types ("Eschatos") or Attributes ("Protos") from the player's GY and/or face-up field to be Special Summoned from the hand.
The Type/Attribute declared to activate the "Archnemeses" monsters' effects must be one that is present on the field; as such, if they're the only monsters on the field, they can only declare Dragon-Type monsters ("Eschatos") or DARK Attribute monsters ("Protos") for their effects. The "Archnemeses" monsters also cannot be destroyed by card effects, and as such are immune to their own destruction effects if their own Type/Attribute is declared for their effects.
The other non-Level 11 "Nemeses" monsters assists in fulfilling the Summoning condition for the "Archnemeses" monsters as all of them have different Types and Attributes. Each of them have two effects: the first effect lets them Special Summon themselves from the hand by shuffling 1 banished monster, excluding another copy of themselves, into the Deck. The second effect allows them to add a different "Nemeses" monster from the Deck, Graveyard, or Banish Zone to the hand, excluding "Keystone", who adds itself back to the hand if it is in the Banish Zone in the End Phase.
Because low-level "Nemeses" monsters have no inherent effects to banish monsters (for their own Special Summon) or set up the Graveyard (for the Special Summon of the "Archnemeses"), additional cards outside of the "Nemeses" Archetype that have these effects is recommended to effectively Special Summon the "Archnemeses" monsters. Inversely, individual "Nemeses" cards can be used as support for other Archetypes that need recovery for Banished monsters.