According to MarioWiki:
*The PAL Hidden Mansion is mirrored from left to right when compared to the Normal Mansion. The NTSC version keeps the layout the same.
*There are more normal ghosts around the mansion.
*Bosses are more difficult, having different attacks. (Chauncey's rocking horses, for example, are much bigger, and swerve left to right instead of going straight). A major change in the Boolossus battle is that the player rides around on the vacuum cleaner while trying to pop Boolossus, making movement more slippery.
*Rooms are much darker in the PAL version; this, however, is only as dark as in the NTSC version of both mansions, the normal PAL mansion being lighter.
*Most Boos have more HP in the PAL version, although some have less.
*Fewer hearts. Locations that have hearts in the Normal Mansion do not have them. Hearts that heal 50 HP exist in the Courtyard by vacuuming the Slim Banskshot-like statue.
*Speedy Spirits and Gold Mice always give up a Silver Diamond when caught, raising the maximum possible amount of money from 142,390,000G to 186,440,000G . Since the requirement to achieve a Rank A mansion in PAL regions is higher than the amount of money in the normal mansion, it is necessary to play through the hidden mansion to receive Rank A in those regions.
*45 rather than 40 Boos are required to fight the final boss.
*Boos are, in general, more agile and difficult to catch.
*Five, rather than three ghosts each, fight Luigi in The Artist's Studio.
