Reactor

The Reactor is the main power plant of the Halberd. It is a large room with Wheelies continuously running within chambers to generate the power, but the part of it that is fought looks like a central conduit of some sort, with a floating crystal in the middle.

Kirby Super Star and Kirby Super Star Ultra
In Kirby Super Star and Kirby Super Star Ultra, the reactor is guarded by a set of auto-defences, including a pinpoint laser gun on an extendible arm, a large pulse cannon, and a series of burners on the floor. According to Captain Vul, the Reactor is invincible unless it shoots itself (via the laser gun), so its defences turn out to be its Achilles' Heel.

When playing as Meta Knight in Meta Knightmare Ultra, his Mach Tornado move can damage the Reactor, and depletes all of its health in one go.

Kirby's Epic Yarn
Kirby encounters the Reactor in yarn form in Kirby's Epic Yarn while travelling through the Halberd on the Starship. Unlike Kirby Super Star (Ultra), it is no longer invincible and Kirby or Prince Fluff has to destroy it by firing on the central crystal himself. The laser gun, cannon, and floor burners are absent, but it is now defended by two long-range flamethrowers - one at the top and one at the bottom. These are defensive as well as offensive - yarn star projectiles from the Starship cannot pass through the walls of flame. Also, the Reactor's defenses are no longer capable of shooting itself. UFOs join the fight every now and then to fire laser beams at Kirby.

Wheelies are not seen in the background, so perhaps the methods of power generation of the Reactor had been changed.