Master Crown

The Master Crown is a seemingly malevolent item that grants its user incredible powers but can possess them if they cannot withstand its power. The crown is seen changing shape to match its holder.

Kirby's Return to Dreamland
The crown is seen resting on top of Landia's head, when the group enter Halcandra via the Lor Starcutter. Once Landia is defeated, Magolor reveal that he wanted to steal the crown and that Landia was too strong for him so he tricked Kirby, King Dedede, Meta Knight and Bandana Waddle Dee into defeating the dragon for him. He then try to fly through a dimensional portal and take over Planet Popstar. He is defeated and the crown take over his body and transform it into some sort of grotesque version of his regular appearance. Eventually, the group defeat the crown and it is seemingly destroyed.

Kirby: Planet Robobot
In the Team Kirby Clash sub-game, Landia serve as an opponent and is stil wearing the crown on its head.

Team Kirby Clash Deluxe
Like in Kirby: Planet Robobot, in Team Kirby Clash Deluxe the crown is seen on top of Landia's head. A Mirror World version of the crown is also seen on top of Parallel Landia's head.

Kirby Star Allies
Void Termina uses two swords with a hilt very similar to the Master Crown in its first phase and summons a reflection of the crown itself in its third phase. In the The Ultimate Choice, Void Termina summons a physical replica of the crown instead of a blue reflection.

Trivia

 * The Crown is implied to be sentient in the pause screen descriptions of Magolor and Parallel Landia (even if it's technically not the same crown).
 * Kirby Star Allies seems to imply that Void Termina is closely related to the crown as it is able to summon multiple Master Crowns and the the eye in Magolor Soul's mouth as well as the eye pattern seen around the jewel of the Master Crown are similar to Void Termina's own eye.