Galaxia

From Kirby - Wiki on Neoseeker

The Galaxia is Metaknight's golden sword. It has intense magical powers, and can only be wielded by Star Warriors. Galaxia is far more powerful than any other sword in the series, and is similar to the Master type of Copy Ability. In Kirby: Nightmare in Dream Land, Kirby & The Amazing Mirror and several other games Meta Knight lends his sword out to Kirby to help defeat the evil forces of Nightmare. In Kirby & the Amazing Mirror, once completing the game Kirby is able to use Galaxia whenever he wants to. This is easily the best power in that game.