Gold, Silver, Crystal, HeartGold, and SoulSilver — Can be obtained inside Mount Mortar. They can also be acquired by defeating wild Horsea, fellow Seadra, Dratini, and Dragonair. Ruby, Sapphire, and Emerald — Can be acquired by defeating wild Horsea and Bagon. FireRed and LeafGreen — Can be obtained inside the Water Path and Trainer Tower. Diamond, Pearl, and Platinum — Can be acquired by defeating wild Horsea and Seadra. Black and White — Can be found on Route 13 and 18. They can also be acquired by defeating wild Horsea, fellow Seadra, Kingdra, Dratini, Dragonair, and Dragonite. Black 2 and White 2 — Can be found on Victory Road, inside the Antiques Shop on Join Avenue, and inside the Wild Forest. They can also be acquired by defeating wild Horsea, fellow Seadra, Kingdra, Dratini, Dragonair, and Dragonite. X and Y — Can be found inside the Terminus Cave. They can also be acquired by defeating wild Horsea, fellow Seadra, Kingdra, Dratini, Dragonair, and Dragonite. Sun, Moon, Ultra Sun, and Ultra Moon: Can be acquired in Battle Tree. They can also be acquired by defeating wild Dratini, Dragonair, and Dragonite. Go — Can be obtained by searching PokéStops and Gyms starting at level 10. They can also be obtained by completing Part “A Ripple in Time” or Special Research.

For older versions of the game, you can trade Pokémon with other players using the Game Boy’s cable link connection by going inside a Pokémon Center in any town and talking to the receptionist (non-playable character) in charge. For newer generations (fourth generation to present), trading Pokémon is done using the Global Trade Stations (GTS). To trade using the GTS, go inside a Pokémon Center in any town, and talk to the receptionist (non-playable character) in charge of the system. You can also use Quick Link to trade Pokemon locally with friends. On Pokemon Go, players can trade with registered friends. Regular trades cost both players 100 Stardust. [1] X Research source Both players must be within 100 meters of each other to initiate a trade. [2] X Research source

Seadra will only evolve when traded while it’s holding the Dragon Scale. Trading without a Dragon Scale will not evolve Seadra. Leveling up and gaining experience will not trigger Seadra’s evolution.

You can choose to skip this step if you prefer not to get your evolved Kingdra back.