Professor E Gadd from Luigi's Mansion tricked Luigi into coming to the mansion the whole time just for the ghost paintings.

Disclaimer: I won't mention any thing from Dark Moon since I haven't played it yet.

I've heard a lot of theories from Prof. E Gadd is evil to is a mad scientist. But I never heard anyone mentioned this before, as we all know E Gadd lived his laboratory nearby the original Luigi's Mansion. Soon King Boo came to that mansion, discovered E Gadd's lab with his other boos and ordered them to set them free. E Gadd then went back in, trapped the boos in so he can lock them in forever so they won't interfere with his portraits once again, but he couldn't capture the ghosts once again because he's old for it and he is unable to do it.

He wanted to make a deal with King Boo to get his portraits again, King Boo wanted anyone to be in his paintings, so E Gadd set up fliers around the Mushroom Kingdom himself for a fake free mansion contest. Mario got there first but was tricked by both E Gadd and King Boo so E Gadd can get his ghosts back. But King Boo tricked and lied to him henceforth angering E Gadd, Luigi got the flier and got there second expecting to see Mario but everything was messed up. E Gadd told Luigi that the mansion was haunted so E Gadd cannot capture the ghosts himself because he is old, therefore he tricked Luigi into capturing ghosts for him and saving his brother. All E Gadd wanted was the ghosts.