The Grouchy Possessor is the first boss in Luigi's Mansion: Dark Moon. He is a white ghost with a horn on his head, and multiple layers of skin, each being a different color. The Grouchy Possessor has infinite HP, as the others Possessors.
The Grouchy Possessor takes control of a spider queen to crush Luigi. He'll have to vacuum a web ball from under the giant spider and burn it like a fuse. This will cause the webbing behind the spider to explode, knocking it back, exposing the Possessor.
The Grouchy Possessor is by default immune to damage, until he raises a Paranormal Shield to ram into Luigi, while protecting himself from the Poltergust 5000's Strobulb flash. After he crashes into a wall (which only occurs if Luigi can successfully trick him into doing so), the Ghost is dazed, and momentarily vulnerable. Only when Luigi fills his suction power meter to full and presses A will the Possessor be forced to abandon his first layer of skin to survive, revealing his second layer of skin which is orange. The ghost will rush go back to the spider (with unrivaled speed), Luigi will repeat this, eventually destroying the Grouchy Possessor, getting the second piece of the shattered Dark Moon.