King Boom Boo

From Sonic Earth

King Boom Boo is the king of all ghosts. He has ghost powers, but he and his ghost minions can lose power because of an artifact with a sun and moon side. When the "sun" side is up, it creats light and they lose power. When the "moon" side is up the become stronger and gain powers. He was defeated by Knuckles at the Death Chamber in Sonic Adventure 2 as a boss. He relates very much like Nintendo's King Boo. When you fight him, you can see on the wall a picture of a Nintendo regular boo, and a regular boom boo.