Kirby's copy ability makes him The Ultimate jack of all trades, and probably the most powerful ever. He can also fly for an infinite time, doesn't need air (He can survive space and underwater), and can eat things 5 times his size. WITHOUT HIS COPY ABILITIES!
The only way the Earth's chosen 4 can defeat it, is by having enough people pray that it can die. Not by brute force, not by psychic powers, only by enough people hoping that it will die. He also corrupts the earth, making people turn evil, or just go insane.