"Hmm mm mm mm mm. You really think you can stop King Boo? You must be in over your head! Nothing can stop him. He is invincible! He's given me special powers that will allow me to finally destroy you!"
--Peach Spirit, in Area 8.
The Peach Spirit is a ghost created by King Boo to confuse Luigi. It bears a good likeness of Princess Peach, but is only a shadow of the real princess.