A soul
Souls are possibly the most important part of the Phantom Mansion games. A level cannot be completed unless all of the souls in the level have been collected. Souls look like skulls with a yellow glow around them. Souls are also part of the story of Phantom Mansion, there are 1,000 lost souls trapped in the mansion. Only by collecting all of the souls and destroying the 7 different coloured masks in the fire in the Black Sanctum can the souls be freed. Though souls look like they could be walked through, apparently they cannot, as boxes cannot be pushed through them.