Mannequins consist of a feminine human torso, clad in what looks like a leotard made from putrid skin, and legs, upon which rest two more legs standing upright, though they noticeably lack feet. The top pair of legs are used for striking while the bottom pair are used for walking. When on the attack, they rub their upper legs together like an insect's mandibles.
According to the Book of Lost Memories, which was released with the Silent Hill 3 guide, the Mannequin is a manifestation of James Sunderland's natural urges and inclinations. The creature is likely manifested because of his frustration with his wife's ailment. Accordingly, Pyramid Head's introductory cut scene has him abusing two Mannequins. Because of this, it's possible that the Mannequin may also be an image of innocence and helplessness being misused or otherwise destroyed by an oppressive, masculine force.