A series is a group of three or more cards that share an appearance in artwork or name, or simply in what their effects allow them to do, but lack the support cards that genuine archetypes possess. Series commonly comprise themed groups used by characters in the anime or manga.
One of the most notable differences between a series and an archetype is the fact that many archetypes, such as "Lightsworn", "Blackwing" and "Six Samurai", can all have Decks easily built around them thanks to their own effects and the support cards they possess. Meanwhile, card series do not have support cards, and building a Deck out of series like "Hex-Sealed Fusion" a hard task. However, this can be also be an advantage, as some series-based decks can be combined with other deck types more easily than archetypes, as they do not have specific support cards that could clog up deck space. An example of such a Deck is Frognarchs.