Seadra is a light blue, seahorse-like Pokémon with a cream-colored belly covered in rough scales. It has a long, tubular mouth, narrow, black eyes, a fin-like ridge above each eye, and spiny pectoral fins. It also has a large, coiled tail. It has a pair of dorsal fins with sharp, cream-colored tips that exude venom. Seadra's venom is toxic enough to induce numbness and even fainting in humans, but it is still prized among practitioners of traditional medicine.
Seadra can swim in any direction while facing forward by rapidly flapping its fins and tail. It catches its prey by spinning its body to create large whirlpools. When its prey is exhausted, Seadra swallows it whole using its long snout. Seadra makes its nest by either wriggling between or anchoring itself to branches of coral under the ocean. After a female Seadra gives birth, the male Seadra will take care of the young. It is markedly vicious and will mercilessly attack those who venture near its nest. During this time, the male's venom also becomes thicker and stronger than usual.
In Mewtwo Strikes Back and its remake Mewtwo Strikes Back—Evolution, Fergus's Seadra was captured and cloned by Mewtwo. The Seadra clone reappeared in Mewtwo Returns.
Seadra made its regular series debut in Round One - Begin!, when Mandi used a Seadra during her first battle in the Indigo Plateau Conference. It battled Kingler and was subsequently defeated.
In Fit to be Tide, Cissy used a Seadra while Ash was participating in her target test. It had a notably sensitive personality. It competed against Squirtle, but the match was declared a tie. Seadra reappeared in a flashback in A Way Off Day Off.
In The Great Eight Fate!, a Seadra was part of Juan's Sootopolis City Water Exhibit. It and Juan's other Pokémon were captured by Team Rocket, but they all worked together to escape.
In Looking Out for Number Two!, Goh saved a wild Seadra from a Sharpedo and gave it the Dragon Scale that he had just found. In return, Seadra assisted Goh in locating a Kingdra that he needed to catch in order to complete a Project Mew Trial Mission.
In Pikachu's Vacation, a Seadra was at the Pokémon Theme Park.
In The Power of One, a Seadra sensed the disturbance caused by Lawrence III.
In Hook, Line, and Stinker, a Trainer's Seadra participated in the annual Seaking Catching Competition.
A Seadra appeared in Snorlax Snowman.
In The Joy of Water Pokémon, three Seadra were living in Lake Lucid. A third was receiving special treatment in a salt bath tank in the Pokémon Center located near the lake.
In The Legend of Thunder!, a Seadra was at the Pokémon Center.
In Pokémon Heroes: Latios & Latias, a Trainer's Seadra competed in the Tour de Alto Mare.
Two Seadra appeared in The Relicanth Really Can.
In Pokémon Ranger and the Temple of the Sea, a Manaphy Egg bounced off a Seadra's head while adrift in the ocean.
Multiple Seadra appeared in Kalos, Where Dreams and Adventures begin!.
A Seadra appeared in I Choose You!.
In Alola, Kanto!, two Seadra were at Professor Oak's Laboratory. A third was featured in Lana's fantasy about the Pokémon she hoped to see in Kanto.
A Seadra appeared in Legend? Go! Friends? Go!.
||Seadra, a Dragon Pokémon. The evolved form of Horsea. Seadra has a violent temperament, and the quills that cover its body can render its victim unconscious.
||Seadra, the Dragon Pokémon. It is known for its horrible disposition, but possesses both strength and speed.
In File 3: Giovanni, Red defeated a Swimmer's Seadra in a battle.
Seadra seems to be based on a seahorse. Its category may be a reference to the Japanese word for seahorse, tatsu-no-otoshigo (dragon's child), which is derived from the myth that a seahorse that lives for a century will transform into a dragon. Its spiky, poisonous fins are reminiscent of a lionfish, its ability to shoot ink is reminiscent of a squid, and the shape of its snout and Sniper Ability are reminiscent of a water gun.
Seadra may be a combination of sea or seahorse and dragon, seadragon, or Hydra (a mythological sea creature).