Sea Serpent

Sea Serpent, known as Sea Dragon in the OCG (Chinese: 海龍 ), are the least populous Type of monster (excluding Divine-Beast), with even the much later introduced Psychic-Type having more members. In the early stages of the game, Sea Serpent monsters had a similar relationship to Fish that Dinosaurs once had to Reptiles; Fish were the weaker, lower-Level monsters and Sea Serpents were the more powerful, higher-Level monsters, or "Big Fish", essentially. This has changed, since Fish have increased in number and utility. Though they are low in number, Sea Serpents tend to be very powerful in WATER-based decks, and they should not be dismissed or underestimated.

Currently, "Atlantean" is the only pure Sea Serpent archetype.

Some major Sea Serpents include "Levia-Dragon - Daedalus", "Ocean Dragon Lord - Neo-Daedalus", "Orca Mega-Fortress of Darkness", "Lightray Daedalus, "Brionac, Dragon of the Ice Barrier", "Sea Dragon Lord Gishilnodon", "Spiral Serpent", "Water Dragon", "Deep Sea Diva", "Reese the Ice Mistress", "Gemini Lancer", "Number 32: Shark Drake", "Number C32: Shark Drake Veiss" and "Lost Blue Breaker".

The only support card Sea Serpent monsters had prior to the release of Raging Battle was "Umi", which was replaced in usage by "A Legendary Ocean", a card that no longer supported non-WATER Sea Serpents. With the release of Raging Battle, however, came the Sea Serpent support cards "Spined Gillman", "Mermaid Archer" and "Deep Sea Diva", with the latter being the first card to exclusively support Sea Serpents. In contrast to early Sea Serpents, which are generally very strong high-Level monsters, the new Sea Serpents and their support focus upon very low-Level monsters and swarming, which actually allows for a viable Sea Serpent-based Deck.

In Photon Shockwave and Generation Force, Sea Serpent-Type monsters are given extra support (along with Aqua and Fish-Type monsters), including "Shark Stickers", "Fish and Kicks", and "Oh F!sh!". After Realm of the Sea Emperor and Abyss Rising, Sea Serpents became competitive with the creation of the "Merlantean" Deck, with the release of important monsters like "Mermail Abyssmegalo" and "Moulinglacia the Elemental Lord", and also a monster that can search for any Sea Serpent: "Atlantean Dragoons".

Sea Serpent have their own Structure Deck, Realm of the Sea Emperor.