I noticed that some of the included mansions in MM2 as well as ghosthunter use custom graphics without an extra copy of Game Data. How is it possible to do this?

Check out Joeb's tutorial on changing graphics to something custom. (He made Ghosthunter.)  ;) He made this tutorial in the days of MM1, but it's pretty much the same thing with MM2.

http://www.actionsoft.com/forums/cgi-bin/yabb2/YaBB.pl?num=1171667389

:-?hmmmm... I already have this extremely helpful tutorial. However I still don't understand how you seem to have custom graphics in a mansion which does not need the changed data.

It's just cool to have your own art while playing your own level, and lets you do almost anything you want.  ::)

What you can do to do so without editing the game data, you open your Mansion file in a ResID software (Such as Rezilla) and create a new category known as "PICT" (capitalized). By looking at the game data in Rezilla you will notice how all the art has IDs. If you want to change some art, you copy the art from the data - edit it in the exact dimensions in a program such as Photoshop - and paste the picture into your Mansion file's PICT category as the same ID as the brick's original ID in the game data. That's how you don't have to make all these changes all the time. :)

Thanks, that was very helpful  ;)