Hector the Reflector

Hector the Reflector is the third boss of Yoshi's Island DS. He is a strange, egg-shaped ghost that resides in a Ghost House-like fort, filled with Boos, possessed furniture, and other supernatural creatures. His fight is unusual, taking into effect the full potential of each screen. When the fight begins, he is invisible on the top screen, but visible on the bottom. Yoshi can peek into the "mirror" bottom screen, find Hector, then egg him on the top. After each hit, Hector throws a flowerpot at the bottom screen, "cracking" it. His Invisighoul minions also pick up furniture and fling it at Yoshi, but he can eat it for more eggs. After five hits, he vanishes, granting Yoshi access to the next level.

Trivia

 * Hector the Reflector gets his name from the mirror part of the battle, he is reflected in the mirror, but not anywhere else.