What Pokemon evolves while holding a Dragon Scale through trade? It evolves a Seadra into a Kingdra. Just trade a Seadra holding the Dragon Scale and once it arrives to the receiver, it will 100% evolve into Kingdra, holding the Dragon Scalâ¦e. HINT: To get a Dragon Scale catch a Dratini, Dragonair, Horsea or Seadra. One of them has a 5% chance of holding one.