First off when you first got the vacumm it sucks weakly. When in the hidden mansion every strong pull deals a lot of damage. The damage you take also doubles in the hidden mansion. That is all I know.
The Previous answer was:Everything is moved to a different location then before. Actually,that's wrong.There are a few differences: -Luigi takes twice as much damage -The poltergust is also more...
The only difference is the difficulty. The game gets harder the more times you beat it. Second time the ghost hit 2x as hard and have 2x the health ,but your vacuum has 2x the sucking power.