Lock Capsule

The Lock Capsule (Japanese: ロックカプセル Lock Capsule) is a special key item present in Pokémon HeartGold and SoulSilver whose use is currently unknown.

Its in-game data is apparently similar to the Manaphy egg that can be transferred from Pokémon Ranger to any of the five Generation IV main series games, and it apparently can be delivered to another game. This may indicate that it has some connection to Pokémon Black and White, though nothing has been revealed at the present time.