Seadramon

Seadramon is a sea dragon digimon that was stabbed into darkness by Facilier in order to provide Dark Cynder with another monster to her monster armada. It has a long, serpentine body, which it uses to wreathe itself around enemies that are coming to attack, and constrict until the enemy suffocates. Naturally, it doesn't have intelligence or speech, and it swims around the Net Ocean leisurely according to its instincts.[4]

Digimon AdventureEdit
During their first night in the Digital World, the DigiDestined come across an abandoned trolley car on the shores of Dragon's Eye Lake, where they decide to spend the night. However, Taichi "Tai" Kamiya and Agumon accidentally strike a large, red, leaf-like object with an ember from the fire, and it turns out to be the tail of a very angry Seadramon, who retaliates by dragging the chunk of shore with the trolley car on it to the middle of the lake. Yamato "Matt" Ishida is the only one not on that part of the shore and leaps into the water to save the others. Seadramon notices him and grabs him with his coils. To save him, Gabumon digivolves to Garurumon for the first time and battles Seadramon, seeing him off. Garurumon It is implied by its Digimon Analyzer profile that the MegaSeadramon in Myotismon's army is this same Seadramon.[5] City Under Siege

A Seadramon appears in the Real World during the Dark Masters reign. The Battle for Earth It disappears back to the Digital World upon Apocalymon's defeat. The Fate of Two Worlds

Digimon Adventure 02Edit
Seadramon is the digivolved form of Betamon, the partner of Michael Washington, an American DigiDestined. He digivolves the first time when the group, who is in Digitamamon's restaurant, is attacked by a Dark Spiral controlled Gorillamon. Seadramon then attacks Gorillamon and drags him underwater, until Togemon destroys the Spiral. The Samurai of Sincerity Michael and his Seadramon show up again later when Digimon begin to appear in the Real World around Christmas time and battle a Cherrymon at Rockefeller Center with help from ExVeemon, Lillymon and the other American DigiDestined's Digimon. Digimon World Tour, Pt. 1

Role in the series
Seadramon first appeared as a reinforcement monster to Dark Cynder in Quest for Camelot. When Ruber's replacement, Cobra, was destroyed for good, the enery wave from his destruction freed Seadramon from it's dark control, and reformed it.