Atlantean

"Atlantean" ( Kaiō) is an archetype of Sea Serpent-Type WATER Monster Cards. They were first introduced in Phantom Darkness, with "Atlantean Pikeman". They later gained more members in Return of the Duelist and Structure Deck: Roar of the Sea Emperor, which also introduced their first support card, "Atlantean Marksman".

Playing Style
The focus of this archetype is to swarm the field with Level 3 or lower WATER monsters with the effects of "Atlantean Marksman", "Deep Sea Diva" and "Atlantean Armed Soldier" to later Tribute them for the summon of their ace monster, "Atlantean Dragon Poseidra", or to Synchro Summon with "Deep Sea Diva" and "Genex Controller", preferably the "Ice Barrier" Synchro Monsters.

Also, the effects of "Atlantean Marksman", "Atlantean Armed Soldier" and "Atlantean Dragon Rider" trigger when they are sent to the Graveyard as cost for a WATER monster's effect, so cards like "Abyss Soldier" and "Brionac, Dragon of the Ice Barrier" would be a good add to the Deck.

Interestingly, the Atlantean effects also activate if they are detached from an Xyz Monster (the effect only requires the monster to be sent to the Graveyard, like "Dandylion"), so a great addition to this deck are WATER Xyz Monsters, like "Number 17: Leviathan Dragon". Here is a list of Rank 4 or lower WATER Xyz Monsters (all current Atlantean that share the effect are either Level 3 or 4):

Monsters

 * Atlantean Dragon Poseidra
 * Atlantean Dragon Rider
 * Atlantean Assaultman
 * Atlantean Armed Soldier
 * Atlantean Marksman
 * Abyss Soldier
 * Deep Sea Diva
 * Genex Undine
 * Genex Controller
 * Genex Ally Birdman
 * Lost Blue Breaker
 * Spined Gillman
 * Treeborn Frog (As a Tribute for "Poseidra")
 * Mermail - Megaloabyss
 * Mermail - Abysspike
 * Skreech

Spells

 * Atlantean Roar
 * Salvage
 * Surface
 * Moray of Greed
 * A legendary Ocean

Traps

 * Aegis of the Ocean Dragon Lord
 * Bubble Bringer
 * Call of the Haunted
 * Fiendish Chain
 * Safe Zone
 * Aquamirror Cycle
 * Spiritual Water Art - Aoi
 * Fiendish Chain

Extra Deck

 * Armory Arm
 * Hydro Genex
 * Sea Dragon Lord Gishilnodon
 * Brionac, Dragon of the Ice Barrier
 * Gungnir, Dragon of the Ice Barrier
 * Dewloren, Tiger King of the Ice Barrier
 * T.G. Hyper Librarian
 * Daigusto Phoenix
 * Number 17: Leviathan Dragon
 * Evigishki Merrowgeist
 * Gachi Gachi Gantetsu
 * Scrap Dragon
 * Mist Wurm
 * Number 20: Giga-Brilliant