From the Super Mario Wiki
Paranormal chains are special white chains appearing in the game Luigi's Mansion: Dark Moon. These chains are found wrapped around certain ghosts, which enhances their strength and gives them the ability to create colored paranormal chains in order to block an entrance. They are only seen in the Secret Mine, in the third mission. In this mission, right before Luigi enters the Gondola, a Strong Greenie, Strong Gobber, and Strong Slammer wearing these chains fly out of the door and flee to separate rooms, but not before blocking the door with their chains. All three ghosts must be defeated in order to remove the chains that block the door in order to access to the Gondola.
Paranormal chains, as stated before, power up a ghost, even if they have already been enhanced with the crystals found in the Crystal Quarry. A normal Strong Gobber's HP is 200, but the Strong Gobber wearing the chains has 300 HP. The Strong Greenie and Strong Slammer are also powered up; the Greenie has 100 HP as opposed to 50, and the Slammer has 250 HP as opposed to 150.